I think people tend to try and justify their choices by deciding that theirs is the best and everyone else is somehow wrong.
All bikes have some purpose, and FS take a lot of the bounce out so can make for a smoother ride, can give better performance on rough ground due to increasing contact with the ground and so on. If you're already doing a lot of stuff with a rigid gravel bike then you may as well go all the way to FS for your other bike as a hardtail sits somewhere in the middle.
Personally, I went for a hardtail primarily due to cost. I bought a good HT for about half of what an equivalent FS would be, and as a bonus it's about 2kg lighter too with space for another bottle cage. I don't do anything too technical so I won't really notice a difference. If I suddenly win the lottery I'll get a good FS too.