If commish really accepted PG13 for McCollum after vetoing above trade (with PG13 as part of it) then it is a bit messed up.
As a 3 keeper league with salaries, the trade in the original post is not unfair. Paul George $62 and Clint Capela $52 are not really worthy keepers. Siakam at $1 is a superb deal, but so is Luka at $26 who is the best dynasty player overall. Actually a fair trade - the fact that it might help one of the teams more in terms of winning this year is irrelevant, it plausibly helps both teams involved especially considering future years too.
I'm not related to this league, just trying to make an objective assessment based on information above.