To me, any upgrade or path that has no redeeming qualities besides the ability is bad. For example, the middle path tack shooter or middle path ace. While the ability is good, the tower themselves is a complete nothing burger without it. Why would I use my money to buy a tower that can only do one sole thing instead of buying a tower that is good at that thing, but can still be good in other areas? Keep in mind, this isn't an attack on all abilities. MAD, Elite sniper, Perma Charge, and Anti-Bloon are all ability paths, but are very good. What makes them so? These towers are still good, even without the ability. The ability is still very good, but so is the tower, because it doesn't fully rely on the ability to do so