And since when are Art Directors, Senior AI Artists, Data Analysts, Executive Producers, Financial Controllers, HR Coordinators, Associate Brand Managers, Cinematics Artists, Communications Coordinators, Community Managers, AI Programmers, or Tools Programmers responsible for gameplay engine bugs?
i would consider all those to be at least somewhat related to solving gameplay engine bugs. there's also the issue of whatever those people are supposed to be doing either not being done or cutting into someone else's time.
dota 2 is also (as far as i can tell, having played ~~60 hours of it) in much better shape, balance and bug wise, than CoH2 and (again, as far as i can tell) has much better analytic tools available to the people working on it. theoretically, once you reach a certain point with a game you only need one or two part time balance devs and occasional time from a programmer to keep a game balanced. RET had only bC on it for several months and it was *mostly* fine. as time goes on the amount of effort required for fixes should decrease as the slop is taken out of the system...
the coding problems, pathfinding in particular, are fairly complicated but the balance issues mostly come down to making changes to a spreadsheet and then testing said changes with a heavy does of judgement involved. more manpower means that changes can happen faster and they're easier to test test, provided everyone involved has decent judgement and is properly supervised.