Just one more quick message from me....
... when starting the game via original "Launch Freespace 2.exe" file,
the main hall loads up normally, although at old, non improved textures.
See in the link

However, when opening the mod via Knossos, it looks like this:

I just realized that the Mjn Mixaels HD halls have been installed.... gonna try removing it and see what happens.
* Update # 1 - nothing happens - with or without the Mjn HD pack the disproportion is the same
** Update # 2 - found the problem - sort of a hardware issue.
My current setup is a Dell laptop, plugged into a 2k display (2560*1080 resolution)
However, to reduce the load and overheating on the system hardware, I'm mostly keeping it at Full HD resolution.
To cut the story short - once I've upscaled to 2k resolution, the Main Hall is fine, the mouse pointer hovers fine, with no discrepancy,
I can log into the Campaign mission.... basically all is fine.
However, when I've tried to disconnect the external monitor,
and run the game via laptop's Full HD display, again the disparity is there.
So, in order to not to break anyone's balls, I guess I'll just give some more time to the game
until I finally assemble my desktop rig and play it as it should be played.
Thank you all and apologies for nagging you.