Minus attack isn't great on most units, but H!Kagero has enough attack to still be useable, so I wouldn't worry about it too much. It especially won't matter if you give her an effective weapon.
As for my summons on this banner I got really lucky with a +ATK -HP H!Mia, who was pretty much the only unit I desperately wanted from this banner. I kind of want to put her on my flier emblem team and replace WF!Hinoka, but I'm not sure how well it will work out. The problem is that in order to optimize her, I'll need to sacrifice said Hinoka to her, and if she doesn't work well on the team I've lost my only flying archer. Not sure what to do really.