True, that might've been the original idea, but "6-8 Encounters per day" is impractical and unrealistic.
True, and, really, it's kinda by design intent.
5e had to get back to familiar class and (especially) spell progressions, that was clearly non-negotiable, so the 5e design greatly increased daily spells, from 1, at first, to 4 at 20th, to 2 at first, 9 by 5th and 16 by 11th, topping out 22. To even bring that close to a comparable limitation, then, they really needed to have much longer days as the game progressed, maybe something like 1-3 encounters at 1st level, 7-12 at 5th, 13-18 at 11th, and topping out at 20-25 encounters/day. But, y'know, sweat spots and all, they settled on 6-8. It makes the game a bit deadly at 1st level, decent starting around 3rd, "too easy" sometime thereafter, depending on the group, and non-functional at very high level.
Which evokes the classic game as it existed from it's earliest beginnings through 3.5, which was, also, very much the whole point of 5e.
You can't get through that many fights in a session, maybe 3-4 if you do little roleplaying and exploration. Then you have to remember and keep track of all spent resources from session-to-session (in my groups' case, a month's wait or more). And if you're doing anything besides a dungeon crawl, it's not realistic that parties will face that many fights in an actual adventuring day. You'll get a couple rolls on a random encounter chart in a wilderness trek - so maybe 1-2 fights. You'll get 1 fight maximum if you're in a city.
I think the better (more realistic) way to have scaled D&D's resources is against a 2 encounter day.
Tracking resource use across sessions doesn't strike me as impractical, but I suppose anything could be too much trouble for some groups, and you & yours may routinely do something I find too much of a hassle, as well. :

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But, the expected 'day' does strain credulity under many circumstances. I like to kludge it by simply disallowing rests - on various pretexts to match the situation - to fit the pacing to the story.
But, whatever the reason for not sufficiently stressing the party's resources, it does explain why the game feels too easy. Because, the way you're playing it, it is.
One solution is to re-balance it around encounters. It's not a complicated undertaking, but it's extensive.
For every long-rest-recharge resource, divide the number of uses by 8, round accordingly (so 1-4 uses you don't get it; 5-12 you get 1/encounter, etc - you can group slots together to get 5+, you have to decide whether you go with lowest or highest slot in the group, I'd say lowest, to be safe), for short-rest recharge, divide by 2.
Remove HD and restore all hps between encounters.