I go back and forth on this. Trey just needs to play football; he hasn't really in the past 2 seasons with only 1 game played since 2019. And I do think this team is talented enough to pick up a rookie QB mistakes to let him learn on the fly. It also just wastes a year of the rookie contract QB, which is your best window to win a title before he costs $30+mil/season.
We don't know exactly what Lance will look like, but we know Jimmy just doesn't have the upside you want from a championship QB. At the same time, this is easily the most talented roster in the Shanny/Lynch era and the receiver corp is talented enough to boost the 20th best QB in the NFL.
I dont know about "easily" with the 2020 team. This year's Defense has some questions still. Lance was a big future cost - I'll be keeping my eye on Fields - of course they would not have known Fields drop that far. Pretty evident though Lance is a superior athlete to Garoppolo - less so evident a superior QB at this point, but already better looking overall. Only a matter of time that Garoppolo hits the pine. I remember Lamar Jackson rookie year when in the Playoffs the Chargers reduced him to total indecision. Still not sold on Jackson even though he's a top 5 athlete in all of football, and likely the 2nd fastest QB I've ever seen besides Vick. You don't need athletics to be great, ala Brady, but it certainly can help.