In my experience, bass traps do help, but they help mainly by controlling bass overhang at frequencies above 40 Hz -- and that’s the BIG traps. Trying to even bass response significantly with bass traps is a losing proposition. But in a room that retains bass, they can be useful for sure.
Still, rejecting DBAs because some people are tireless boosters is like rejecting vitamins because some think they cure everything. It is not logical to discard a proven approach because some adherents are obnoxious (not that we have any of them here).
I thought Erik’s linked essay was useful except for that tack. In particular, it pointed out that adding subs is not plug-and-play, if one wants to get good results. Good crossovers, some kind of EQ, and phase matching have been indispensable, when I’ve done it.
