Engie could use some more tools so here we go.

First change would be a new skill called Rocket boots. It would go where Bugmans best is in the tinker tree Bugmans best would be moved to Core in tinker tree at level 25. Rocket boots upon activation Knocks back anyone behind you a medium distance and would be a channel for 10 seconds 50% movement speed increase plowing through enemies anyone you plow into also gets hit with friction burn.
Second Change would be a quality of life change and just eliminate Well Oiled Machine tactic and just make Turrets insta summon. Trying to run without this tactic in places like city or fort where aoe is high is just a waste of time. Even with the changes to survival for the turrets they still die very quickly. Well Oiled Machine would become a new tactic that reduces the cool down times of skills for your turret by 50% and it auto attacks 50% faster. This would also work on the next change as well.
Third Change M1 Autoloader eliminated and a New M1 called BFG goes in its place. BFG summons all 3 turrets at once for 30 seconds the wounds of the turrets are doubled and they can use all Core skills you have access to. Gun turret would use all Rifleman core skills, Bombardment Turret would use all Grenadier core skills, Flame turret would use all Tinkerer core skills. If they get killed before the 30 seconds is up they self-destruct doing aoe damage and knocking down anyone within 30 feet.
Fourth Change Make Flak Jacket the self armor buff a non enchantment buff so it can't be shattered off. On live it had a 20 stack buff that would lose stacks as you got hit. Now any monkey with nerfed buttons and shatter enchantment can remove it without thinking about it.
Fifth and Final change Change Extra Powder tactic 3 point tactic in the Grenadier tree to make Firebomb and Sticky Bomb hit all targets in 20 feet of the target. Rename the tactic Extra Boom BOOM!