Quite the contrary. Flat damage affects Pet builds with more Pets than ones with fewer critters running about.
So the nerf will hit skeletons harder than other builds.
Neither Skeletons nor Hellhounds fit “strongest” or “highest damage”.
No more toxic than Ghol Blightfiends.
And a Pet Battlemage can do SR 75: Bottle Fwuffy - Pet Battlemage
That says nothing other than Pets being safe even on meme builds for SR pushing.