That the game has been designed to work roughly like Mearls says has been clear from the get go. That most people actually do not play like this has been clear about as long.
I agree that the design goal is absurd. In all my decades of playing RPGs, I don't think there has ever been an in-game day with six to eight combats. I don't think how they tested it, but in my experience this simply is not a thing that happens at all, let alone commonly enough to be a sensible design benchmark. And of course having spells like Leomund's invincible bunker that allows players to dictate safe rest whenever is utterly insane is such a paradigm.
But be that as it may, that's the logic the game is based on, and I think a lot of people run into problems by simply ignoring it. There have been countless threads where people complain about things where this is the underlying cause. If you don't want to run the game the way it was designed to be ran (and I don't blame you, me neither) then you actually need to make some adjustments. The easiest one is to use gritty rests or sanctuary-only long rests or both (I use both.) This is not exactly a panacea, but it is sort of "have you tried switching it on and off" type of thing. It solves most of the issues, and you should try it before doing something more complicated. Basically what it does is make the your "daily budget" your "adventure budget." You have this amount of resources to solve the whole situation, before you pack your things and go home to properly rest. And it has the added benefit of being somewhat more verisimilitudious. It is utterly ludicrous that you can be beaten within an inch of your life, be lying on the ground bleeding to death, but as long as you pull though, you'll be perfectly fine the next day.
All this being said, I think seven medium fights is still way too may, and they will in most part be boring pushover fights. I usually opt for 3-4 way more challenging ones. Granted, they still are pushovers a lot of time, as at least in 5.0 monsters are weak, challenge rating is a lie and characters are immortal. I doubt that using 5.0 encounter building rules, in mid levels and beyond six medium fights would deplete much resources beyond the player patience. They made encounters way more deadly and boosted monster in 5.5, so that has probably been at least partially fixed, but I really don't know as I have not been bothering with encounter building math in a long while. I just throw some crazy stuff on the PCs and watch them triumph. I'm sure that with 5.5 boosted monster I end up accidentally killing them at some point.
A week from the gritty realism variant rule was too long - the bbeg was going to complete his ritual, and whole armies could force march!
I think this is a feature rather than a bug. It means that if you take long rest before "solving" the situation, you're basically giving up or at least having the direction to significantly evolve into unfavourable direction.
As for other fixes. The issue with getting rid of attrition altogether, is that then fights risk becoming even more meaningless as the victory is quaranteed and nothing is lost, or alternatively you need to ramp up the deadliness of the game up significantly. In attrition game loss of precious resources can be the cost of a fight gone badly, but if resources refresh for each encounter, only mechanical cost available is character death, and after revivify comes available, a TPK.
Why do we even want attrition based design for more than one combat?
Because it gives the DMs more tools to pace the game.
If everything resets after every encounter (like with a 5mwd), the stakes are only during one combat. You either win or loose, nothing in between. No costly victories, no defeats that are not to bad.
A combat has no impact outside of itself.
That's why you want attrition based design. So combat matters afterwards, too.
Yes, exactly this!
As for gamey suggestions such as requiring twenty rounds of combat before long rest or similar, I think those are a non-starter. It is simply a terrible idea if you want to have any sort of connection between the fiction and the rules instead of treating it just like a hack and slash computer game. It also creates weird incentives such as making it impossible to play smart by trying to avoid combats, or making picking up fights with random weak NPCs to fill the "combat round gauge" and optimal thing to do. Roleplaying games are bout the fiction, and the characters inhabiting that fiction. The primary role of rules is to represent the fiction, and these sort of attempts utterly fail at that.