I think even a little charge generation (even at 20%) for Blast Cannon is a good thing. Quality of Life for Cannoneers.
Fusillade draining charge per shot could work pretty well.
Blast Cannon needs something else than the +28% fire damage debuff to make it worth investing in, right now its pointless to put 15 points into it when you can just blast everything easily with Fusilade (For end-game, which is what i focus on), Blast Cannon should either be made a Charge spender OR a debuff ability with/without a cooldown, blind doesnt work on any bosses as Salan already informed us ages ago so the tier bonus is useless for end-game activities.
Tier 1, +5% physical and fire damage, +2 debuff duration.
Tier 2, adds additional +10% physical and Fire damage, +2 debuff duration.
Tier 3, adds additional +15% physical and Fire damage +2 debuff duration.
Ends up with a grand totall of +58% fire and physical damage debuff for 10 seconds, that would be worth 15 points imo since it boosts the damage of other abilities.
Would be good to allow Blast Cannon to give charge at 100% so you had an actuall cannon attack that you can use to charge your bar.
Fusilade should get a dmg boost with 2 more rockets from the tier bonus( 6 rockets at tier 3) since its lackluster compared to Emberquake and Flame hammer. The range can be annoying, but usually solved by getting the sledgebot out and tank stuff for you, works on bosses aswell for a while untill it gets crushed ^^, would enjoy if it had a 0 range tho, but i guess it wouldent be as unique of a skill if it was?. From an end-game perspective i view the cannoneer as sub-par since the damage is lacking and to do well you need to re-position yourself all the time which adds to the time it takes to kill stuff.
Fusilade tier bonus:
Tier1: 4 Rockets are released per Burst. +5% damage per charge. Uses 1 charge if available.
Tier2: 5 Rockets are released per Burst. +10% damage per charge. Uses 1 charge if available.
Tier3: 6 Rockers are released per Burst. +15% damage per charge. Uses 1 charge if available. (Each tier bonus does not stack with eachother, so its only +15% damage per charge when you take the Tier3 bonus for a totall of +75% damage bonus on a full charge bar)
Allowing for Burst Cannon to gain Charges and for Fusilade to gain damage bonus per charge gained would change the end-game for Cannoners to use Blast Cannon then switch to Fusilade (If the dmg bonus from the charges will be worth it, dunno if it will compared to just spamming Fusilade). Engineer wouldent do too much damage simply because it takes some time to gather charges unless you are surrounded by enemies and use Dynamo field a few times, but most bosses do not spawn more than 3 mobs and using Dynamo field means you arent doing any decent damage for a few seconds anyway.