Excluding Kat, she's probably the best 1vs1 character period.
The difference is, her execution barrier for a lot of her top techniques is quite high so most people don't think she's that OP because most people can't pull off what she's really capable of.
For instance, she has an up throw that leads into either a 140AP burst or a level 1 super but it's really hard to pull off consistantly to the point where even the best FP players either don't go for it or mess it up often when they do.
If she touches you on the ground, potentially if she had at least 40AP, that's a death as she can combo you into an 80-90AP sequence into level 1 similar to Dante. The difference being that she actually has the tools unlike Dante to pressure air campers and force them on the ground as well as the safest air poke in the game that's also a combo/kill confirm.
She's not underrated. Everyone knows that she's the best in 1v1... right below Kat.
She's not that popular since you can pick up other high tier characters and go a lot farther in a shorter period of time. Characters like EC, Kratos, Nariko and Sackboy are a lot easier to 'master,' so they get more shine.
PSN: Lakizzle23 Mains: Dante (Self Acclaimed Best Ever) , Good Cole (Rusty)