Not the best because you want to be doubling your opponents, not get doubled and lose more HP.
She's supposed to fulfill a bulky role to take out enemy reds, and occasionally take a hit from a blue.
Her Luna skill more than makes up for her lower attack. At 31 base speed, threats like Anna, Nino, Rinda, Aqua, Felicia, +Speed Sharon, +Speed Kamui will all be able to double on you and kill you.
Red units like Lyn, Lucina, Sheeda, +Speed Ryoma, +Speed Marth, will be able to do more damage to you because you're doubled.
Katua in particular suffers from trying to figure out which stat to + and which stat to -.
She's one of the units you might prefer neutral because it maintains her bulk, or a +Resistance/-HP one because it lets you take a little bit more punishment and the overall HP lost isn't too bad since you were going to get OHKO by a Takumi anyway.