The terrain rules are not the final arbiter. There is a lot of nice looking terrain where what is a window or not is questionable at best. I played on a table that had building with large acrylic windows, and I just assumed it was like any window you can shoot through. Opponent had the complete opposite assumption. Neither of us was trying to game it for advantage, just completely different views on what it was. We talked it over and ended up treating it like a wall. Best option is to discuss all the questionable stuff pre-game, but it can be hard to notice.
Tbh I actually really hate playing any table with windows, so I make sure to confirm what is or isn't a window pre-game. That's partially due to how my group first played the game, where every terrain piece had an open window for aesthetic... It was ARO city. Miserable games. Sorry to hear that your tournament went badly, though.
There’s plenty of little improvements that make the game more enjoyable: Making sure all stairs and ladders have a ”back” so there’s no los through them. Closed windows that are staggered (can’t see through the building from the outside). Open doors. Large base planters where the plant isn’t to ”wild” making low-vis zones clear if you want to use those rules. No los underneath containers or other terrain pieces. Proper los blocking terrain for antennas, consoles and the like. No los through fences on board walks and the like. No large overhangings (ie gas stations). Small details like this makes a huge difference and removes a lot of the common issues. It is usually easy enough to draw los as it is.
I agree with all of what you said, but there is a lot of really high quality terrain that looks extremely nice.....but still have many of the issues you described. I think all of these issues can be cleared by just discussing it pre-game. Locally we play that models can see through 1 window, but not 2. This allows to be used, without creating the nightmare of cross-table AROS through 3 building + 6 windows.