Most rooms don’t need acoustical treatment.

Yeah, nothing really matters except just keeping on buying newer, more expensive gear to impress your friends. Don’t worry about cables or the AC mains either. 
And don’t be confused because some of the greatest studios and music halls in history utilized scientific processes together with some very brilliant craftsmanship to create a believable soundstage. It’s all an illusion. 
Well, that’s unless you care about your listening space reproducing beautiful realistic music. :)

For 41 years, I lived in a 2000 sq ft loft in lower Manhattan. The 1200 square ft open area was the listening space, it had an irregular shape with tin ceilings, 60% of the eastern wall covered with huge windows, a brick wall behind the system, and hardwood for the floors. It was a lively listening room.

Three years ago I moved to a townhouse in Newburgh NY that we gutted and restored. My 500 sq ft office in the attic doubles as a listening area. Dormers on one side, a gable on the other. After 15” of rock wool insulation was put in the ceiling, and 6” in the walls, I covered it up with burlap instead of sheetrock.

Books and LPs line almost every wall.
The sound in my Newburgh home is dramatically improved from my NYC home. Almost like buying a new stereo. And I got this improvement without hiring professionals (although our architect did have a background in acoustical science), just by using basic common sense with regard to what most of us know about how sound works.

Is it perfect? No. But it’s way more than good enough. I’d rather listen to music than worry and tinker.

You do not need any room treatments. At least not while you’re using your headphones.

My room settings are now so good that all my 7 headphones are not on the level of the room on any count...

Then think twice....

 and he told me that unless I wanted to get a much more significant number of bass traps that would heavily change the look of the room (and my marital status)

You could use Helmholtz tubes and pipes to transform the acoustic  decresasing the bass traps to only a minimum level.... But it is all up to your wife acepting a set of 3 groups of tubes in the living room...  😊

For sure the biggest asset in audio is not the gear at all it is using a room ONLY for audio...

"The acoustician knows the problem but can’t imagine the solution, so he doesn’t ask the DSP engineer.”

Helmholtz did never own a dsp system but he created room acoustic with bottles...

I imitated him and my room with a 500 bucks system trash all my 7 headphones and rival any systen i had listen to...

You are right in your post about the great tool DSP integrated will be .... I just want to make a "nuance" that primitive methods using helmholtz tubes and pipes to set the room/speakers together using EARS could work... I did it at no cost...

The orchestra fill my room with each instruments in his tonal sphere...