Parmandur
Book-Friend
I'm saying that the constant low-level discussion of issues caused directly or indirectly by the 5-8 encounters a day format is the evidence.
People aren't saying "I hate 5-8 encounters a day!". I agree there. They're saying "Paladins are overpowered", or "My encounters aren't very threatening!" or "My encounters are too deadly!" or "I can't really challenge the PCs, they just breeze through stuff!", or "I feel like I'm a bad DM even though I've been running stuff for 30 years!" or "long rests are too powerful, they should happen less often!" or "Let's make healing slower, this is ridiculous!" and so on. They don't realize the reason is 5-8 encounters/day. They don't make the connection. But that's basically the (narrow) majority of design-complaints about 5E right there.
As I noted in an edit, I have two friends who DM who don't follow the 5-8 encounters thing, because they've been DMing for 30 years and it's never worked like that (definitely would be fair to say through all of 2, 3.XE and 4E, somewhere between 3-4 encounters per day was the average, with plenty of 1-2 encounter days or the like - and 4E it was clear 1-2 was already a problem, but again, only I seemed to actually follow the guidelines). I tried explaining it to one of them once, and he didn't quite get it. He's not thick. He's a long-time DM. He just didn't really think it could have that much effect. But you and I both agree that it does. Further, he's happy with 5E. He's in that 90%. So am I! That's what you're not getting. But I'd be a lot happier if they had designed either around 3-5 encounters/day, or gone with a system that didn't rely on a fixed number of encounters/day. And the only people who'd be unhappy with that are the A2s of the world, and I'm not even sure all of them would be, because resource-drain stuff can work with lower numbers of encounters too - indeed, it's much easier to tune for that than vice-versa. What we have is a system that is not quite outside the acceptable margin of design.
Just as a personal aside, I find it totally obnoxious because it's very hard to tell a story which makes sense and isn't set in a dungeon which includes 5-8 resource-draining encounters in 16 hours. I'm not sure you even disagree there. But if I don't, everything is a breeze and whilst the players like that occasionally, I can see that, long-term, after 4E, which was balls-to-the-wall hard because of the 3-4 encounter/day design and the far, far, far superior ability to gauge monster threat inherent to the system (5E is terrible at that, though not as bad as 3.XE which was ACTIVELY misleading - using the numbers in 3.XE would leave you with a worse understanding of threat than eyeballing the monsters), they miss it if I don't at least try to challenge them with the stupid 5-8 thing. But it feels so naughty word weird - and their instinct, honed over decades of D&D, is to long rest way sooner than 5E wants them to.
And let me re-iterate the most cogent point here:
You keep saying WotC would just change if this was really a problem.
To that I say, no, because they can't change this. This is baked into the very most basic mathematical assumptions of the system. It does not play well with anything less than 5 encounters/day. It plays "okay", acceptably.
But WotC can't change that because it's baked in. They'd need to re-bake the cake. Make a 6th edition. With different classes, spells, recovery options, monster design, and so on. So that WotC stick with it is only evidence, by any means, that it's not enough of problem to cause massive badwill by going to a new edition already.
You make some intriguing points, but when push comes to shove, tuning the game around a maximum threat rather than minimal seems best suited to purpose.
And as for how things used to be...the older modules I've seen seem to fit the criteria of the 5E workday?