Sensible trade for both teams. The Celtics now need to attempt to trade Thompson, re-sign Fournier and sign a rotational PG. Meanwhile, the Thunder continue their master class on re-building.
Obviously nothing is guaranteed and this might not ultimately end up as good as it looks potentially promising, but I'd still rather have a bona fide cornerstone in tow (Gilgeous-Alexander) and umpteen high quality assets/flexibility than be the rudderless Spurs.
Samanic has yet to prove he's an NBA player and wasn't a high enough pick or pedigreed enough prospect at any point that any team would or should hand him a starting job.
Collins (Markkanen is far more likely) wouldn't "thwart" his development, as barring the outcome of the draft they don't have a backup option and I'd be surprised if that changes during the draft.