Nobody is saying he will shoot 43% he is a 38% career which is solid, last year he was at 43% and everybody agrees he won't accomplish that again. Your point is about weakest link, Barnes is not the weakest link... Spurs we lack perimeter shooting that's quite straight forward. Sochan cannot shoot untill proven otherwise, Champ is a SF, KJ, Bryant can't shoot. If Sochan suddenly starts to hit some 3s we can discuss but right now Barnes is useful especially if Spurs get into the POs. Victor can compensate Barnes flaws on defense, nobody is capable to compensate lack of shooting especially this year where Victor wants to operate more inside... We have Dylan, Fox, Castle, KJ, Sochan who wants to attack the basket, for that you need space. You have 3 guys other than Victor who can shoot 3s above 37%: Champ, Barnes, Vassell and your point is Barnes is the weakest link
If you'd want to improve spurs right now without considering future or development you trade KJ, Sochan before Barnes.
As you said Barnes is just that a nice vet in last year of his contract spacing the floor and bringing scoring, that's exactly why he is here.
I won't enter in your Lyles delirium... I did not even remember this dude was a Spur