"Less", as any educated person would know, refers to the quantity of a quality or thing: "We had less snow this winter than last" or "He is far less intelligent than he thinks he is." "Few" refers to quantity: "I have never before see so few people at a funeral -- not even the corpse showed up" or "Fewer than one in a million play a zither in B#."

Therefore, "lesser" can hardly be the opposite of "better" (although I give you credit for using the comparative).

Good -> bad
Better -> worse
Best -> worst

"He was a bad man, worse than Billy the Kid, the worst man I ever met." Compare that to "He was a bad man, lesser than Billy the Kid, the worst man I ever met."

No, the correct term would be "worser".