Pathfinder WOTR solved both of the issues you mentioned. You cannot spam rests since there is a corruption mechanic that inflicts penalties for resting too much out in 'the world' and respeccing on the harder difficulties is completely disabled. Off the top of my head, Tactician not allowing respecs and having an 'tadpole in brain' mechanic where you are plagued with nightmares or something so outside of camp you only have short rests or something are low hanging fruit options Larian could have used, but they seem to be allergic to learning from other CRPGs.
Yess, indeed, I have been thinking on why my runs of PF:KM and PF:Wotr seemed so much harder on unfair (and I beat both games TWICE on that difficulty) and then it hit me: yes, you could multiclass the default set of companions, but within reason given by their stat spread and base classes (which is as much as I liked Sosiel's personality... he was kind of overshadowed by Daeran and Ember combat-wise). Not to mention that corruption mechanic and the fact you could get attacked while camping out in the wilderness effectively wiping your group cause you got caught without buffs...
BG3 should've indeed taken a page from those cRPGs when it comes to the overall encounter design and difficulty design (unfair KM/wotr is particularly nasty early game, but enemies still remain a threat throughout the campaign, even so called trash mobs). Imho, what they should've done to encourage long resting is - disable short rests on tactician, disable respecs, possibly leave 1 respec for the MC for the entirety of the game (or have 1 respec for MC/companions so you'd have to choose who to spend it on). Add to that tadpole brain rot corruption. Make actual passage of time matter. But yeah, like you said, BG3 devs seem to be allergic to taking inspiration and learning from other cRPGs, or the devs just don't play any PC games themselves, or don't play cRPGs at all due to lack of time, maybe? I dunno, half of the time it seems like BG3 is trying to reinvent the wheel, instead using what's actually working.
BG3 doesn't offer previews, so everyone that does not know Song of Rest is at lvl 2 makes due with what they have. And the game without spamming Long Rest and respecs is still way too easy for it to be anywhere near mandatory. My first playthrough was a Warlock on release and I already didn't need to rest so much it broke a lot of my companion interactions from missed scenes.
Don't get me started on BG3's shit lvl up UI, again, something what games had solved ages ago, games as old as NWN1...
Also, Larian's goddamn insistence on tying important events to long resting. Ever since EA I've been conditioned to rest every 5min, sometimes even 5 times in a row to ensure nobody has nothing new to say (once they're fully rested with camp supplies I just spam partial rests, since they fire off those events too). Like shit, I could probably go with only 2 long rests, maybe even 1 through the entirety of surface lvl of act 1 on tactician... Meanwhile the game expects you to have rested at least 5 times before reaching the grove, ridiculous!
