Sonny Vaccaro says he believes Caitlin Clark could have gotten a much better deal from Nike -- telling TMZ Sports he's sure the former Iowa superstar could've inked a pact similar to the one Michael Jordan got back in the day. The shoe industry legend, of course, knows all about the deal MJ received -- he was the one who helped negotiate it. And, when he heard Clark only received $28 million over eight years to be with Phil Knight's co., he was surprised it wasn't more. Vaccaro tells us she could've landed a contract that not only gave her more annual money -- but also allowed her to take a cut of every Clark-branded item sold ... just like Jordan got with his initial Swoosh agreement in 1984. "She should have gotten a piece of everything," the 84-year-old said, "just like Michael Jordan." Vaccaro believes there were plenty of people to blame -- everyone from Clark's reps ... to other shoe companies who dropped out of the race and allowed Nike to come in with what appeared to be on its face a company-friendly contract. "I'm saying to you," he said, "they messed up. They should have held on to the last drop." Clark, though, doesn't seem too disappointed ... $28 mil, after all, is a ton of coin -- especially considering she's only set to make $76,000 from her WNBA contract this season. And, hey, she gets her own signature Nike shoe ... which we're sure she's thrilled about.