Please remember the Karlach kiss was most likely not UA's at all and there because of a bug in testing. It didn't work unless you switched Karlach's body to body type 2, the animations were broken, and they've removed it now (not to mention, it didn't make all that much sense?)
I fail to see how repurposing the Karlach origin kiss for both AA and UA doesn't make sense. I am aware that the kiss was bugged when people first saw it in her origin run, and it possibly could have been only meant for AA but I think it would work with UA as well. Astarion comments on the pc's neck quite often so him grabbing players face to look at their neck before kissing could work well with him on a UA. This is why I think softening his expression for that kiss would make the most sense. This would also then make sense on to why he is so rough after his ascension because it would then showcase that he had always been a little bit rough when it came to tav/durge for kisses.
This is just my suggestion though, if Larian wanted to give spawn 2 brand new kisses along with adding the new evil bite kiss then so be it. I just want equal content for both routes that's all.
