Even if I've convinced you that incarnate is a good thing when designed well, I still need to defend lack-of-variance
The most popular Commanders need to get through 2020 without reprints, and then Ill relax
Black (Common), Silver (Uncommon), Gold (Rare), Red-Orange (Mythic Rare)
There are some Slivers still available to players on a budget, as well as some Sliver-centric spells that can kick Sliver Swarm up a notch
For that reason I think Niambi is fine as a commander but better in a deck that has access to Black, such as Sisay, Weatherlight Captain
Create a token that's a copy of target permanent, except it's a 4/4 Dragon creature with flying in addition to its other types