I do think that long rests should be limited somehow, and that short rests should be increased in frequency to compensate. It just feels so cheesy to long rest 3 times while scouring a dungeon.
long rest in dungeons should be outright penalized.
Pathfinder: Kingmaker did it more properly. You can take long rest in dungeons. But can't hunt for food while doing that, and you get significantly increased chance of been attacked in the middle of long rest.
BG3 made it too cheesy, where party can easily return to camp regardless of where they are. I would simply deny long rest in dungeons completely. If player still thinks he really need a long rest for the party - he can leave the dungeon, but...
Fast travel in dungeons also should be removed.
You still would be able to take long rests, but would have to travel long way in and out of dungeon every time. That would drive players plan their progression in dungeons relied on short rests, and other forms of healing (spells, and large stock of healing potions)