The second amendment was passed when there were slaves, and I guess the 2A supporters at that time didn't see it as contradiction.

These people aren't mellowing on their position on 2A; they're instead starting to think "Hmm maybe some of these 'people' shouldn't be considered fully people from legal point of view ..."

I agree that they don’t necessarily view it as a mellowing of their position, but as a matter of policy the net effect is the same.

All my life I’ve heard conservative talk radio types (and more recently, conservative influencers) chant “shall not be infringed” as a mantra and oppose any restrictions whatsoever (at least, post-Reagan; see the comment down-thread). That old state of affairs has subtly changed.