Now I know you are underrating Zoro. Luffy has used G2/G3 anytime he has fought a none fodder yet you claim he has better base than Zoro. He has better CoO but that has nothing to do with their physical speed. CoO doesn't make the user faster.
Luffy grizzly magnum, his strongest G3 attack, only destroyed Pica head. Zoro's haki none name attack cut the upper part of a larger Pica body in half in an instant like it was nothing. Zoro's none haki 1080 cannon destroyed a larger portion of a larger pica.
The purpose behind the gear is to give Luffy more strength, power, and speed.
Why would he bother using base when G2 is so casual for him?
So Luffy has better reaction times, better mobility and can run his way out from the centre of an explosion but he is slower than Zoro.
Luffy is a goofy character and has many low showings because if he didn't One Piece would be 300 chapters shorter, but his high showings are far higher than Zoro.
G3
Pulverized Pica's head, and that was where Luffy aimed, if he aimed centre mass it would have pulverized a very large area. Zoro was in the middle of a named attack, his attacks don't suddenly become far less potent if he doesn't shout every single slash he needs to do. Slashing some rock in half is less impressive than turning it into dust, and requires less help from Kings punch.
Also Elephant gattling is stronger for AoE for obvious reasons and would have fodderized Pica very very easily, this was PIS.
All G2 and G3 has done since the timeskip is get embarass by anyone strong. Hyouzou blocked him,Doffy was destroying him before gamme knife, Katakuri wrecked him, couldn't destroy has much has Pica like Zoro did,couldn't get out of Ulti grip,, Cracker fodderize him, Yamato blocked etc.... Stop ✋
He fought Katakuri for a long time in G2 or G3, anyone weaker than Katakuri who Luffy has fought with G2/G3 is irrelevant.