Ultimately, I don't think that this matters much in the end. AFAIK, when you buy a recent'ish Ubisoft game from Steam and launch it from there, it'll also launch a modified version of the UPlay client just to run the game. BUT since the game is forever tied to Steam, it will ALSO launch Steam if you try to run the game just from the UPlay client alone.
I don't see Ubisoft changing this for EGS so regardless of if you buy an Ubisoft game from Steam or EGS, you're just adding another needless client that has to be run just to play an Ubisoft game that needs the UPlay client anyway.
Unless the game has a deep discount from that platform, just buy the damn game from UPlay and save yourself some headaches.