1) Nested prefabs and newer C# versions was great, everything else has been a wash.
2) Hell no. It's slower to start, slower to import, slower to compile.
3) Nope, and our artists would (rightfully) quit on the spot.
4) Nope. DOTS doesn't really cover our case, and their rendering solutions are needlessly fragmented. Actually, everything is needlessly fragmented: unity versions, adding a package manager, deprecating their network stack without a replacement, it's just a mess.