This isn't really a fair comparison, as Mahomes was a highly touted QB and we (as has been stated many times in the past) genuinely just didn't know what we had in Tatis - he was 17 when he was traded. Easy to look back and Monday morning quarterback it but it just is what it is at this point.
Also on Mahomes - everyone forgets that if we hadn't picked Trubisky the most highly touted QB in that draft class was actually Deshaun Watson - we should be glad we at least dodged that bullet.