It will get expensive once you reach cannoneer at rank7. SP cost is high, especially if you spam the 5s cd cannon shot. SP:damage isn’t great, you will have to use a lot of pots, like the swordie fencer class. Don’t take the armour break attribute on Cannon Blast, it increases SP cost a lot for a 3s armour break with low chance. The best damage booster is the Bazooka stance. Bazooka will lower your mobility a lot. You cannot move and you cannot use non-cannon skills during bazooka stance. Cannon skills deal +25% damage vs plate armour enemies. The damaging cannoneer skills are very easy to use and cannon skills get innate +AoE. Cannon attribute +block pen is okay too.
Cannon skills depend on your off-hand cannon damage stat. Most of your remaining archer rank skills use your main-hand crossbow damage stat. You will have to invest into 2 weapons to be strong unless you build a cannon-only build such as arch2 hunter3(only growling) appraiser cannon2.
A2-Sap3-App-Can2 is strong at AoE with broom trap and cannon skills. If you like cannons, get cannoneer. If you like bow, go mergen.
Some vids to view playstyle/skills:
Old vid of a2-sapp3-rogue-can2 PvE earthtower click here
A2-sapp2-wugu2-can2 at new fantasy library click here , and click here
Rang3-scout-rogue-cann2 solo dung 290 (older vid too) click here , and at Earthtower solmiki with team click here
Wugu poison is strongest with a high str stat because only the spread-poison of wugong gu can crit. Usual wugu build is arch2- x - wugu3 - falconer1 - mergen. You could go arch2-sapp3-wugu2-mergen or Arch2-sapp2-wugu3-mergen too (+AoE attack ratio gear). Wugu best skills are throw gu pot, wugong gu, needle blow — jincan, zhendu. Detoxify is useless, just buy antidotes at the Item Merchant NPC.
Qs3 cannon2 is also something to play around with either get appra1/scout1/falc1 as filler on rank6. But so far sapp3 appra1 cannon2 is the best aoe cannon build with just proper skill management you wont run out of skills to use on earth tower runs as sub dps, can only be called as main dps if you over funded it like trans7 and up emengard/lolo/solm cannon and invest a lot on xbow as well.
I think theres no one using bazooka stance, atm its really bad. I guess it will be good only if imc makes a quick set up attrib for it or something like that. But a cannon user knows he/she shouldnt use bazooka in any given situation.