User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-82.178.206.137-20180615103908/@comment-10330822-20180621034108

She may simply be too young right now. Remember, Rias is a baby compared to Sirzechs, who is centuries old.

Besides, I would prefer her not to just become a carbon copy of her brother. It's much nicer to see her develop special techniques and combo moves to power herself up rather than just make her as OP as Sirzechs is.