yeah I would think so as well, best handled as one unit.
I think problem is the low frequencies of mains are not compensated. I mean, lets imagine we have DBA setup in perfectly working order, no hints of standing waves, just pristine bass. As the sub system handles itself regardless of mains we can now abstract it away and inspect / imagine the mains alone and how they interact with the room. Mains high passed at 100Hz would excite the modes normally around the 100Hz, if they do not make a plane wave and are cancelled at back of the room. To circumvent on would have to make the plane wave up to schroeder frequency I guess, 16 sources per wall? now the furnishing and all would affect how it works I believe, unreachable.
SBIR is nasty, affects mainly above 100Hz, unless speaker is ~1m out from the wall, which is the most usually recommended distance. All first reflections combined, in general, tend to make huge dip >100Hz. Luckily the first reflections are gone in milliseconds and many more come in and compensate
I believe you the bass array gives some relief on this, but would reason it doesn't eliminate SBIR effects from graphs, perhaps helps with audibility and thats all we need.
After all, its impossible to get anything "ideal". Its fun to imagine the stuff on the ideal perspective though
here sim of ideal mains speaker 1m away from wall, same as middle picture above. Then two ideal subs on the wall behind to emulate half of a bass array is added. Without delay on the mains the problem is still there. With delay its easier, but a power response dip occurs and it's basically still there. To remove SBIR we'd need to prevent sound from mains reflect from the wall, cancel it with the subs. So actually the subs would need to be delayed, polarity flipped and so on, which wouldn't still help as the overlapping bandwidth is so small, so we need to get mains further from the wall to get SBIR lower in frequency and leave the high pass out, and now we excite the modes and so on. Mo problems. Perhaps FIR precondition filter could help, remember to add to back woofers as well
perhaps easier to embed the main speakers into the front wall as well, than go this route. Make the whole front wall a speaker, plane wave all the way up to schroeder. Problem with this is that plane wave is mono.
How about making the front (and back) wall perhaps 8 full height line arrays of say 3" full range drivers? make plane wave as high frequency as ear tells, then shade away the rest.. well or just go outside to a field when in need of pristine sound