It looks to me like the big traps are making the room dead under 30 Hz, but you have ringing at 45-48 Hz and it's dead again at 80-100 Hz. There is another apparent mode at around 130 Hz.
I would probably remove some of those bass traps in the corners and see if the room will start to reflect some of that 80-100 Hz bass. Also, subwoofer (or another sub), properly placed, might balance out the ringing at 45 Hz with the suckout at twice that. But I'm rather thinking you have a bit too much absorption.
I also see a dip between 800-1000 Hz, which is right at the upper limit of what I would try to EQ out without knowing the anechoic data for those speakers. But I might still nudge it up in that region and then listen.
That's just what I would do. I see the deep bass deadness on the waterfall as much as on the frequency response. Usually, the ring (the part of the waterfall diagram that comes out at you) is more pronounced at those frequencies, not less. I'm not used to seeing no ring at all in the deep bass, and that's why I think it's overdamped with bass traps. The diffuser works at higher frequencies, but it's diffusing an echo, not absorbing anything, so those frequencies are still allowed to decay naturally in the room. Not so the deep bass (except for the resonant mode at 45).
I don't do Roon, but somebody does, I'm sure. But that's what I'd be experimenting with no matter what equalization tool I used.
Rick "who'd do a little mirror testing with straight left and curved right wall first reflections, too" Denney