According to 17Lands stats, the only cards in the A+ bracket for the format, meaning they have the highest associated winrates, are Deviant Skytech and Unforgiving Overtake
Hangarback Walker does have a way to add +1/+1 counters to itself, but at the cost of tapping itself , taking it out of a combat role
Certainly it is better (compared to itself) in the powered cubes but perhaps it isn't relatively as good in the meta
Orzhov has a bunch of excellent ways to make token creatures such as Bitterblossom and Call the Coppercoats, and giving them vigilance and lifelink is fantastic in Commander
The rules complexity is considered low, while the strategic depth is medium, making it accessible to a broad range of players
Cards like Pokmon Center Lady or Full Heal can quickly remove Sleep if your Pokmon is affected