In 15 years of this, living in Vegas for 8 and tied in with some of the biggest groups around, I've never seen anyone get down $1m at one Vegas sportsbook for a MLB parlay. Definitely haven't ever seen it with a local bookie. That indicted guy has been around forever with his 50centjuice site but there's no way he was taking $4m bets on MLB team totals. I met him twice in Vegas.
Phil Ivey used to get down MLB for a Russian syndicate out of NY and he had unlimited credit at every casino in town. Most anyone would take was 100-200k on a normal side or MLB total, so he'd have to go get down at 5-6 outs for one game's targeted amount.
Nor have I ever seen a book take a 5-leg same-game MLB parlay for 4k to win $10m
Not saying the stories themselves aren't true, as I've seen some pelicular Ohtani stat lines, but the money wagered just isn't realistic.