I haven't played the game, including ranked, in over 4-5 months. This was mainly due to cannon rushes are just too potent and a pain in the behind. Honestly I find the range on the cannon to be the main cause of the problem.
If the range was reduced to 6 instead of 7, the cannon would need to be moved closer for it to be effective and would give Stalkers and marauders a neutral range. But in all honesty this would leave the air attack gimped compared to the other static air detectors. In honesty I think the photon cannon should have two separate attacks where the ground attacks had a shorter range it would nerf cannon rushing without too many knock backs.
the Problem is cannons absolutely SUCK vs tier 1.5 and tier 2 units, because they all have gimmick !@#$ like 6 range, 20 damage, blink, hardened shields, fast regen, or 13 range, etc.. If you make cannons any weaker they won't be worth making for anything EXCEPT cannon rushes...
It's already the case that cannons cannot even stop their own value worth of certain units, and I don't even mean seige units, I mean a-move "mover-shooter" units.
If not for being able to block up with buildings, the cannons would not even be good vs early Zerglings or Zealots.
Cannons out-ranged most units in Broodwar too. I think they had 6 range there, and everything except the Tank, Lurker, Reaver, and Dragoon had 5 or less range.
Lurkers had 6 range but needed to be burrowed to attack, so Cannons still beat Lurkers pretty well, unless you had a mob of the Lurkers, which is unlikely.
Static defense is supposed to beat everything in a "stand-up fight" except Siege Units and Siege Equivalent units. Because it cannot move, it is supposed to be much more cost-effective than units. There are already too many units that beat cannons cost for cost,w hen they are supposed to be a zone denial that the opponent is supposed to be forced to "deal with it" somehow.
If you want to blame something, blame the ridiculous tier 1.5 and tier 2 units in the game, like Marauders, Roaches, and Immortals. With their insane defensive and offensive stats, those units are what caused Cannons HP and Shields to be inflated back from the 100/100 of BW to the 150/150 of Starcraft Vanilla.
Are cannons too good vs Tier 1? In some situations yes they are, but they HAVE TO BE, else there would never be any worthwhile reason to make them, because they'd suck even harder vs everything else.