"Gravity is a theory" - you say that gravity is a well-substantiated, well-supported, well-documented explanation for our observations. That is the meaning of word 'theory' in science. I didn't say that gravity doesn't work on the small scale - of course it works. I told you that GTR doesn't work well when we achive quantum level, because this theory is used to explain macro scale events and it perfectly explain every observation on macro scale.