Tatis' start to the season was basically prime Babe Ruth playing SS so you had to think it wouldn't last at that level, but he's still been worth 6.5 WAR in his first 140 MLB games. Acuna has been worth 2 WAR in 43 games this season - basically a 7.5 WAR seasonal pace.
This has been a sport in the last decade where elite prospects have come in and dominated quickly at a young age - Trout, Harper, Machado, Bryant in the wave before this as well. I don't think that it was unfair to expect that Guerrero would walk in and be a 5 WAR All-Star type asset at this stage, given that that seems to be par for the course for a player with his billing. That he's plugging along at 1.7 WAR through 180 career games and 0.2 WAR this year as a 1B/DH is pretty disappointing relative to those expectations.
Thankfully Bichette has come in and actually performed at that level.