Defender Mastery is great and one of my personal favorites, but some paths don't come close to the other ones. All the paths, I feel, should be equally effective in combat. The weapons is a different matter, because they are completely separate from each other, but i wont go into that Here are some of my improvements:
Slicer:
Slicer is good and one of the best weapons you can choose from, but fire route's ability(fire tornado) is basically useless. It's hitbox is very small and when you do hit someone(usually unintentionally), they don't take a lot of damage. The hit box should be larger and maybe slightly more damage.
Baller:
Baller is great and very beginner friendly. It's easy to hit, does damage, and knockback. The routes are pretty good, but bubble route falls behind the other ones. While spike route does insane damage, and homing route can HOME, bubble route's only gimmick seems to be that the balls can't bounce. Sure later you can get balloons, which can bounce, it's really just weaker homing. I suggest adding a popping mechanic, so when you hit someone with the bubble, it pops and ragdolls(like bubble ability). The balloons could also pop after a certain amount of bounces or once it despawns, this time with a much bigger attack radius. This would give bubble route it's own unique gimmick.
Crusher:
Crusher is my favorite of the four and is very well done, each of the routes is unique. If I had to say something it would be to make juggernaut even more of a juggernaut(less ragdoll time and even bigger. Hammer and all).