As far as how she got released:
I'm kinda numb about it. Since I played Fate/Go since its japanese launch, I kinda accepted bait banners as part of the mobile gacha experience. While I understand how people can see it as a dirty move, part of the issue is the playerbase, since I saw so many players assume that she would be the tempest rewards or GHB and I think that they hyped themselves too much and the fall was even harder thanks to that. (It doesn't help that I feel like the players are a bit spoiled in FEH too)
As far as her performance as an unit:
In my opinion she is a good example of powercreep, but let's face it, Reinhart and B!Lyn are far too oppresive in arena, and I think that amount of power is necessary for a sword user to not be a liability. (Sigurd and Arden are quite busted too, while Tiltyu and Deirdre are more in line with what was already there)