With everyone's balance issues aside, this is nicely done. Though, you're asking to balance something that is, by its very nature, overpowered (Slivers), and if you're familiar with the story of Magic the Gathering's various worlds, every single entity or group that tried to control the Slivers was eaten by them. Casually.
Volrath tried with mechanical slivers. Venser tried with BETTER mechanical slivers. Eventually Volrath just parked his plane of existence overlapping Dominaria and eliminated the queen. That ended well. (Spoiler: It didn't)
The Riptide Academy attempted to resurrect all the species lost in the planar overlap, and to control the Slivers they created the Sliver Overlord. It worked well for the Slivers, since they almost need a queen, but for the Riptide? Yeah, they were hunted down by almost everyone in creation and branded as criminals.
In every instance that Slivers turn up they are overpowered deck-destroying player-eating machines. So if the Queen seems a little overpowered to all of you, well, tough. FireInTheSky is just doing the source material justice. The Sliver Queen is the central hub of a race that has plagued the various realms of Magic the Gathering's multiverse since their inception. The Queen is a monster, an engine of destruction.
I would say that this build isn't powerful ENOUGH, but then again, the Queen's true strength is her brood. They are ever a part of her.