"manually gzip static files yourself", yes, but like you probably saw few times, some frameworks compile multiple .css files that they got into one file, they could also just gzip them
The only question is: Is it possible to set those or similar rulesets in litespeed? I know that litespeed probably cache those static files after compressing (to decrease cpu usage), but still there could be some really big files that exceed cache size limit and that could be very helpful.