Aiyuk isn't in the same tier as Jefferson, Lamb, Chase, etc., but these arguments don't make sense.
First, just absolutely brutal brutal resorting to fantasy analysis. You keep calling him a borderline top-10 receiver (he's clearly a receiver on the rise) like that is a BAD thing, that's actually excellent, and say $28 million per year (which would be 6th highest in the league, soon to be 8th after Chase and Lamb get contracts). The 8th highest contract for a borderline top-10 guy sounds very reasonable.
This analysis highlights his explosiveness and efficiency
https://www.espn.com/nfl/story/_/id...9ers-trade-wr-steelers-pay-contract-extension and he runs a full route tree very well.
I keep going back to being cool trading for him because I'm tired of watching incompetent offense that can't produce points. I want to see more touchdowns, more explosive plays, and upgrading the talent at wide receiver--whether it's Aiyuk or someone else--will help that.