No, I understand it quite well.
Straight from your link:
Anybody who claims that "Having Kevin Love on the roster isn’t actually an argument as to why Key’s RAPM, EPM, etc is so bad", or that " is unfamiliar with the inherent flaws in these stats.
Did you read this part? I recommend you read this section and then determine whether or not it takes into account that he plays with Love sometimes. The issues you mentioned are not specific to a Key-Love pairing. If you’d like me to explain I can, but please do read this following portion:
What does adjusted plus-minus incorporate?
Every time segment a player is in a game, adjusted plus-minus tracks:
(1) The other nine players on the floor,
(2) The length of the segment,
(3) The score at the start and at the end of the segment.