To put it into perspective:
SP costs of cannon skills were not adjusted when they added overheats.
Firstly, Bazooka was nerfed down to +50% cannon skill damage and +50% basic attack damage. Unlocking the +50% cannon skill damage adds +20s to the cooldown of bazooka (base cooldown 0 seconds, base SP cost 0).
Then bazooka was changed from a 10 point skill to a 1 point skill. (maxes at 1 point, to free up more points for other skills)
Bazooka received some synergy with a few skills:
-Bazooka near Quarrel pavise = knockdown immunity
-Bazooka added skills: pavise, running shot, steady aim, overestimate, praise, circling, sneak hit, evasion, call, aiming, zhendu, detoxify. Naturally, detoxify and praise are useless.
Second, the damage buff patch. I will show values so you can calculate/decide yourself whether cannon lost damage or damage was buffed with bazooka nerf.
This is Steam TOS cannon shot Lv15 damage value and SP cost:
Remember to add the current +% damage of bazooka before nerf to the skill factor%.

Cannon after-patch cannon shot Lv15 damage value and SP cost:
Remember to add bazooka after nerf to the skill factor%.

Shootdown is the anti-air version of cannonshot so the values are the same.
Cannon Blast Lv15 Steam server

Cannon Blast Lv15 after patch

Remember to add before-nerf bazooka bonus and after-nerf bazooka bonus when comparing damage values.
Steam cannon barrage 10

After patch cannon barrage 10

The buff to the cooldown of smoke grenade is good, nice disable for ground mobs now.