No doubt here.
Boasting of a much better attack of 130 over Mightyena's 90, as well as higher speed (75 over 70), it thoroughly beats Mightyena.
In its base form.
Meaning it can mega-evolve. Which Mightyena can't.
By mega evolution, Abol gains Magic Bounce, a tremendously useful ability, and its attack sky rockets to 150, and its speed reaches 115, leaving most opponents far behind. With access to strong moves like Play Rough, Sucker Punch (STAB Priority and works exceedingly well with Magic Bounce), as well as boosting in form of Swords Dance, there is no room for doubt.
Now, I'm not sure which game you're playing, but whether you have access to M-Absol or not, it is still better than Mightyena.
Just a heads up, if you're playing RSE, then Dark moves become Special type and Absol still wins with base 75 Special Attack over Mightyena's paltry 60.