Great question. The January consensus in beta was that Guinevere was OP and the way to bring her back towards the “great hero” range was to reduce her dark buff. Which SG has finally done, but only after people have spent gems to summon her and rare mats to ascend her.
I think of the changes to Ares and Alberich as “down-tweaks” not “nerfs”. The changes are relatively small (relative to original proposal, thanks to feedback from beta testers) and don’t, to my mind, materially change their value. I don’t think anyone will regret having ascended them. Maybe not so with Guen, especially in light of the March HotM (also Holy).