Also to comment on #1
I don’t think that being ‘machmir’ like a da’as yachid amongst the rishonim or acharonim always fits one of the two categories you set forth. However, I see many yeshiva guys following what used to be rejected shittos amongst the classic seforim merely to be “safe” according to every possible position. This is very different from removing doubt when there is a safek – here there is an accepted psak that one is choosing to transcend.