it doesnt feel like it has much grunt
It's true, the 150 Aerobat has poor performance. I have not been lucky enough to fly the other two types, but I am confident that those aircraft are easier to fly aerobatics.
However, I learned limited aerobatics in the Aerobat. I learned to coax the most from the meager power. Consider the skills you might gain mastering aerobatics (well, in fairness, limited aerobatics) in an underpowered, rather sluggish aircraft.
Presuming equally competent instruction in whichever type you choose, perhaps start your training in the aerobat, (and get a few more hours per cost), then transition to the more capable types, when your skills have shown you the shortcomings of the Aerobat. The skill to nurse an underpowered aircraft through decent aerobatics will be less learned, when you can power your way through them instead.
In any case, well done pursuing this aspect of flight, you'll always be a better and more competent pilot for it!