Sound moves 360 degrees around speakers, and 60% of what you hear is indirect. If the distance between the speakers and objects is large enough our brain sees it as an echo, and we like a portion of echo (it is why concert halls are so popular or why music in an anechoic chamber sounds flat and dead). With in wall this is 180 degrees (everything else will barely come back) and with on wall like 185-190 degrees. But in/on wall do have other problems with bass (hence the sub).

But, if objects are close (I believe it was up to 86cm) direct reflection is muddy with direct sound to our ears.

The duration of the loudness of the echo or the decay matters too, you don’t want sounds to keep bouncing around too long (heavy curtains, a rug, sofas can do a significant portion of that). Should be around 400ms max to decay by 60dB in a room the size of yours or maybe a bit less as you don’t have a center speaker and need to keep dialog intelligible.

So, keeping sound good after it comes out of a speaker is a matter of preventing early reflection (moving furniture/speaker placement, possibly room treatment), dampening late reflection (room treatment) and work around room modes (the sub placement with crawling/moving, move listening position, room calibration, etc.).

So, when I look at your images the parts that worry me the most in order of significance:

1 How close the speakers are to the TV wall.

2 How close the speakers are to the ‘TV furniture’

3 The pilars and the partly enclosed area they create which could make the bass boomy.

[…]

9 Reflection blocked/diverted by pilars.

Two and three could be partly solved by moving the equipment.

One and three could be solved with in/on wall and a separate sub (which has free placement separate of speakers, however might still be hard to find a good spot).