unlimited long rests need to be addressed, tabletop is balanced around limited resources and as BG3 is now, you have full resources for every fight.
Yes, but it's still optional. The design allows players of different skill levels to make their way through some of the longer side quests, essentially choosing their own level of challenge in how often they choose the long rest.
Maybe it will be gated off somehow at the highest difficulty setting, once that's in the game? Right now though, the player can set exactly how difficult each dungeon or similar encounter can be. It makes the game more approachable for newbies. I know that might make hardcore D&D players upset, but Larian is trying to sell to a wide audience here. At least you're not forced to long rest on some schedule. You can choose to play it more hardcore if you want.
There also the issue that the mindworm story seems to only progress on long rests, that may not be a good design.
That's a potential problem, yes. It might be that the story progress isn't just based on number of long rests, but maybe also player XP progression?