I think the problem is that he doesn’t really bring anything to the table, at least nothing that’s new. Tharja is arguably better in most cases thanks to her prf and access to IVs. A resistance boon brings her defense to 33/33 with her prf, and her speed is an effective 44. Her HP is lower, so she can’t run Infantry Pulse, I guess, but she has more potential for big damage.
And I think most of the hatred is because of his speedo.