Like most of my fellow colleagues contributing to this forum, I've tried all sorts of footwear "solutions", but found no universal answer. I have, however, learnt by experience that footwear selection is very much a personal preference and also depends on anticipated weather, conditions underfoot, etc. In an attempt to keep as light as possible, I walked the Hebridean Way in April, taking only fully ventilated running shoes (Merrell All Out Crush Tough Mudders). Vast areas of bog in the Uists confirmed my decision to tolerate wet feet when walking was the right one. They quickly dried on the drier sections and using waterproof and insulating socks within wet shoes at the end of the day to keep feet dry and warm worked well. The problem was the flat profile and lack of arch support on the many long sections of road walking, which caused gastrocnemius and soleus tendonitis, which almost stopped my walk.
Despite this reasonable result, I tried some walking sandals for the very wet Pennine Way terrain in September this year. Unfortunately the Merrell Blaze sandals mashed my feet really badly, even though the superb ventilation and drying ability was a plus point. That said, the worst boggy areas now have long stretches of industrial stone flagging to keep above the bog and for the majority of the rest of the time a good bit of hop, skip and jump would keep the feet dry if wearing even mid-ankle boots on the Pennine Way IMHO. At Horton-in-Ribblesdale I met my "trail angel" and swapped the sandals for ventilated shoes, but it was a mistake to have no other footwear. Because I didn't use any accommodation other than a tent, shoes stayed permanently wet-through. "Water-proof" socks didn't cut the mustard and although I finished the PW in 13 days, my feet were mashed. I've reflected on this and offer my advice, for what I think might have worked better...
I'm not a fan of "boil in the bag" membrane boots, but that said I'm getting on really well with some Meindl "Response" lightweight GTX mid-boots. They are about 800g. I'm sure other manufacturers make similar. These are light enough for me to take the additional weight penalty of taking my Merrell Tough Mudders in my pack. These only weigh about 350g. Most of the time the Meindl keep me dry and I find them supportive and very comfortable on all terrain. I don't sweat so much at 58 y/o, so not a problem, but if the Meindl get wet, or if the weather takes a turn for warm and dry, I'd swap out to the Tough Mudders and carry the Meindl, which might then dry out. I'd swap between the 2, depending on terrain and circumstances and I'd have footwear for camp. It's surprising how often a drying room is across a muddy farmyard, so if you only have one set of footwear and it's damp, it's not going to get dry. I appreciate that I've said continually wet feet are "ok", but if your feet are mashed, it's not ok. Skin is far more fragile if wet and after a while you crave dry feet.
I reckon my 2 pairs of footwear equate, roughly, to the weight of one pair of leather boots. In the past I had some full-leather Meran GTX, which were heavy, let in water and performed badly for me. I also ditched the flip-flops for wearing around camp - light but useless.
For shorter trips (up to 7d), where I can rely on the weather forecast and conditions are going to be dry, I'd take my INOV-8 Roclite 315s as the only shoe I would need. For longer trips, with an uncertain forecast and the prospect of bog, I'd take the weight penalty and take the mid-boots plus vented trail runners.

Only footwear I’ve found to be waterproof on a day in long wet grass is full leather.

I have used light weight cloth boots and mountaineering sandals and they are great unless you are prone to plantar fasciitis which I am. Before I started getting the dreaded heel pain from extensive use of lightweight foot wear I enjoyed walking for miles along the coast, in the sea, in my mountaineering sandals. No socks so no wet as your feet dry as soon as you are out of the water. In trainers you get tired later in the walk than in heavy boots
But to avoid the heel pain I have to wear 3 season boots all year and I find Altberg boots keep my feet dry, mostly, especially with gaitors. I get damp sock rather than soggy ones if I am walking in wet grass for a long time.
I have done the whole Southern Uplands Way, notoriously wet, without getting my feet wet. If you are expecting wet feet because of the terrain or weather, a spare pair of dry socks is nice to have.

The question has vexed many here I'm sure, ourselves included, and there is no easy answer. Much depends on the location and kind of terrain you walk in and, as always, a certain amount of luck.

Assuming no manufacturing fault, if you primarily walk on clear paths and easy terrain like most Lake District routes and/or you're lucky, the waterproofness just might outlive the guarantee.
If you often walk in rough pathless terrain ploughing through vegetation like heather and tussocks and/or you're unlucky, it may fail on the very first outing. The numerous tiny sharp tares from the vegetation build up where the footwear bends, particularly below the laces near the toes, and get scrunched about - not good for membranes.
In practice it could be anywhere in between.

I've heard that membranes sandwiched between layers of leather are the most robust, sounds reasonable but I can't confirm because I never wear horrid clunking leather boots.

After many years using membraned flexible lightweight footwear, we don't expect them to remain fully waterproof for more than a few of our backpacks. More frequent replacement is just one aspect we accept as part of the game.

Matthew's approach is to abandon the idea of keeping water out and just tolerate it with footwear that drains easily, there are quite a few hikers in agreement it seems. We've briefly tried that but it isn't for us I'm afraid, at least on many of our particular backpacking routes including much of mid-Wales. The assumption by many seems to be that your feet get wet only briefly and occasionally, always followed by a convenient dry stretch where they have chance to drain and dry. On many of our past backpacks, our feet would have been sopping wet the entire day without a minute of respite.
Other things being equal, wet feet are far more likely to suffer from problems like rubbing and blisters, especially on long days.

Incidentally, since abandoning awful boots over 20 years ago and using flexible footwear (current Merrell Moabs with nice wide toeboxes), we've never had a single blister between us or even a hint of one, despite doing 20-odd mile days on occasion. Think about it!.

Having lived in mid wales over 30 years, I have spent much of the time walking and running through bogs in the rain, I have never bothered with waterproof footwear accepting that I will soon be wet anyway - from a knee deep bog or deep stream. The water is going to go in anyway, so I prefer it to be able to get out easily rather than stay in there, anything waterproof would have to be up to my knees to be of any use.
Non waterproof trainers for me in wet conditions, the water goes in and the water goes out again, once you are used to wet feet I have never found it a problem.

Its probably been asked on here many times but as a new member I am interested to find if anyone has ever found a waterproof walking boot? I currently use the Salomon GTX Mid boot which is super comfortable but as waterproof as a sponge. I am now on my 5th / 6th pair, i like the boots as the comfort outweighs but the lack of waterproofing ( yes I clean the boots and frequently apply the suggested re-proofing) my Leather boots which are slightly more water resistant are my Altberg Keld boots but these also fail on those walks where the terrain is wet, again i clean and apply the alt berg approved wax all to no avail, the boots still leak ! . I have tried many types of boot over the years, Brasher, Berghaus, Scarpa, Karrimor, Nee Bee, Meindl ( the latter being probably the worst leather boot for water proofing ) In wet conditions I use gaiters and waterproof trousers so its not a simple case of water running down the leg into the boot. Am I just unlucky or is the waterproof boot lable a myth ? I have just accepted that on a long walk in the wet my feet will not stay dry. If there is a waterproof boot out there ( not a wellington ) I would be interested to hear. Thank you Mal