Is Attack+/ Speed- Olwen good

She has some... pretty low attack to begin with and her speed is one of her redemptive quality.

I'm going to say 'no' as she works solely as an assist or, in my case, that magic spike bomb she uses when Glacies activates.

She's got some great resistance, but I can't imagine using this Olwen outside of Horse Emblem.

Comparable to a -atk Rein. Not great. Kinda useable if you want to build her, but still just ok. If the - was on HP Def of Res she'd be a lot more useful as a Quad hitting unit or doubling with a blade tome. Decent with Hone Cav, but still less than ideal.

If you have a only a -atk Reinhardt then it's better, and on a horse team, she's still a better bladetome mage than Reinhardt because 31 speed with LnD and horse buffs is very respectable still.