I always felt the cannons were fine, because they were a last defense and crushed that one random person (or Chaser) trying to rush your base - that was what the cannons were good at - aiming at a few targets. The current cannons were already not very effective at dealing with more than 3 people running into the base at once, and had key blind spots.

With the nerfs:
- Oppressors/Brutes would just sit outside the north entrance and destroy the core without getting hit
- Brutes can MegaBeam both cannons down together and take minimal damage because only one cannon will barely reach it
- Healers would just out-heal the cannon damage; one can attack a cannon outside the base and the gunner will be stuck with two choices:
1) Focus the healer and stalemate due to healspam while other players file into base.
2) Attack the players rushing the core while getting killed by the healer.

Imo, the cannon nerfs pretty much defeat the point of them. They were already ineffective in a large push.