Gaara was at a handicap because of the fighting zone and Deidara had intel on Gaara but Gaara didn't even know the dude's name. I rewatched and re-read the anime and the manga Gaara would have won the fight if he wasn't distracted and exhausted his chakra by protecting his village but Deidara is a lethal ninja and didn't prepare enough clay for the fight and didn't use C4 during the fight but Gaara is more skilled at long ranged fighting and Deidara wouldn't have the chance to use it. So Gaaara > Deidara everyone stop thinking he won the fight. Deidara in an open area could defeat most ninjas though, just saying.