... regressed significantly from his 1st to 2nd year.
Sticking to the debate on Fernando, he actually played a fair amount in his rookie season (2019-20), for a second round pick. 56 games, 13 starts, 12.7 min/gm, 52% FG%, 4.3 pts, 3.5 rebs. That is not bad for a 2nd round pick. The thing that happened though is ATL added Gallinari, Capella, and Okongwu (pick #6 overall) for the start of 2020-21. There were no minutes for Fernando. Rookie first round pick Okongwu basically replaced Fernando and played 50 games, 12 min/gm, 4.6 pts, 3.3 rebs. Just for perspective, Grant Williams is a career 4.0 pts, 2.7 rebs in 16.5 min (14 starts in 2 seasons). Semi Ojeleye is career 3.5 pts, 2.1 rebs in 14.6 min over 4 seasons (24 starts).
I suspect that what the Celtics are hoping is that it is not that Fernando regressed but rather they just liked their first round pick more than their second round pick (whose production was actually no better than what Fernando did his rookie year). Young players tend not to regress without some external factor. I don't know what potential Fernando has or what kind of player he will become but I am surprised by how many are willing to declare him a bust so quickly when he has essentially produced about the same as Semi and Grant, when given the chance.
One other trivia item, in the 2019-20 season with the Hawks, Fernando played a total of 133 minutes on floor with Jabari Parker (24 games). They were +20 in those minutes, the second best 2-man +/- overall.