I hate what they did with her character in "Endgame,
In Endgame she was simply wallpaper, something to be looked at and pretty much nothing else.
I also agree with your assessment of the scenes with her and Mulgrew. Amazing to watch, when you consider that during the show Kate resented the introduction of the character. I was heartened to hear that in the last 2 years she's come to reassess her own response to the addition of Seven, and has comes to terms with it.
As for me, although I really liked Kes, I loved the introduction of Seven of Nine. It gave the show back the "conflict" that so many craved. I "appreciated" her despite the outfits (not quite my cup of tea.) which is a testament to the woman's acting ability.