You thought correctly. BAT updates tons of textures on aircraft, maps, and objects, and these changes do fall under the category of graphical improvements. If memory serves, it also has some small effects changes—some damage smoke effects, I think? I forget exactly.
What you probably mean by "graphical improvements", though (shaders and the like), are beyond the scope of a mod like BAT.
For general graphical improvements,
try graphics extender:
https://www.sas1946.com/main/index.php/topic,58926.0.htmland also try ReShade:
https://reshade.me/Both of these can be used to make the game's general appearance look more realistic (and they can even be used both at the same time). GE provides a more in-depth graphical overhaul, completely redoing atmospheric and object shaders to both be much more beautiful, but is kind of laggy and glitchy and also incomplete, and doesn't work with every computer. ReShade is much more surface level, and provides a lesser degree of improvement, but is more stable, customizable, and optimized.
For effects mods, just browse the "Effects" board:
https://www.sas1946.com/main/index.php/board,76.0.htmlTry things that catch your eye.
Note that effects mods must be placed in the folder corresponding with the BAT module you're using. For instance, a mod placed in the #WAW3 folder will apply to and only to the WAW module.