Sound meter + equalizer = problem solved?

Sound Meter: Yes.

Speaker/Signal Level Controls: YES

basic, more specific frequencies, a lot of frequencies. Depends on your space, and taste, and need for 'good enough' or perfection

EARS: yes, last,

find a preferred adjustment to the 'best flat' you achieve with meter/controls. Old dog, hear less highs, perhaps boost highs beyond what the meter 'hears'. Wife with ears that hear highs more than you do: cut the highs a bit.

Bass: seems weak, or muddy, no matter what the meter 'hears', boost or cut bass a bit.

There are two frequency responses:

- Direct to the listener

- Room response

Which one are you going to fix with EQ?  ... and therein is your quandary.

room acoustics/Fletcher Munson problem

I’m not even sure what this means. My advice is consistent here. A good sounding room and modest to no EQ is ideal, especially with subwoofers and trying to plumb the depths (16-40Hz) of output.

EQ is a lot better than nothing in rooms with tremendous bass peaks.

Room acoustics and EQ are not 100% equivalent, they do generally, both affect tonal balance. A very bright, reflective room can be made to sound tolerable by a basic tone control.

Treating the room to reduce mid-hi level reflections will make the bass appear, like a capsized ship coming out of the ocean at low tide.

There's also things you can't do with EQ.  Diffusion in between and the sides of speakers is very important for filling in and improving imaging.  A controlled resonance time makes your brain work less and ears to see more.  Bad room modes can only be fixed with a combination of EQ and bass traps.  EQ alone can't fix it.

(Lets the swarm crowd jump in here and take over the thread).  Swarmers, I'm talking in context of the OP's post.

Best,

Erik

Sorry should be clearer. Fletch/Munson and room acoustics are two different  cases, not just one, where equalization is a big part of the solution.

Digital room correction is like a spare tire, hopefully you never have to use it.