Harper told John Tomase of NBC Sports Boston he's always been a fan of Betts, who has one year of arbitration left before potentially becoming an unrestricted free agent after the 2020 MLB season.
"Just like [the Los Angeles Angels' Mike] Trout did," Harper said of Betts beating his contract. "Mookie's an incredible player. If he has an opportunity to make more money than I do, then I hope he does."
Trout signed a record-breaking 12-year, $426.5 million extension with the Angels shortly after Harper inked his deal with the Phillies, but Harper's contract remains the largest in free-agent history.
The 26-year-old Las Vegas native has endured a couple of slumps during his first season in Philly, but his overall numbers remain solid. He's posted a .254/.373/.492 triple-slash line with 26 home runs through his first 124 games after seven years with the Washington Nationals.
Harper discussed his mindset when it came to testing the open market rather than signing a long-term deal with the Nats like Trout did with the Halos, per Tomase:
"For myself and other players, you earn that opportunity to go there. You're locked in for a long period of time with one team once you get drafted, and then you have an opportunity to go and listen to other teams and see what they have to offer. It's a fun time, it's a good time to feel wanted, and Mookie is going to be wanted by a lot of teams and I think Boston is going to be one of them."
Betts is the reigning American League MVP after posting a 1.078 OPS with 32 home runs and 30 stolen bases in 2018. He hasn't been able to match that production this year (.892 OPS), but he still ranks 12th in the league in WAR (4.8) among hitters, according to FanGraphs. He had an MLB-best 10.4 WAR last season.
In March, the four-time All-Star, who turns 27 in October, said he doesn't plan to sign a new deal before testing the market.
"That's exactly what I expect," Betts told reporters. "I don't expect anything to happen till I'm a free agent."
He'd have a good chance to surpass Harper's $330 million as an unrestricted free agent, especially since Boston will likely try to do everything in its power to keep its organizational cornerstone.