Tom has been training grappling/BJJ since age 7. If Jones couldn't do anything with Santos, Reyes, and Miocic (who is not known for fighting off his back, none of them are actually), then why would he do better with a bigger, stronger guy who has been training sub defense for a long time?
Tom doesn't need to win by submission. He needs to avoid the takedown and if he does get taken down, he needs to get back up without serious injury. And he needs to KO/TKO Jones. It's not at all impossible, I think it's relatively likely.
Against Stipe, he did not show the gas tank to be wrestling-heavy for consecutive rounds, maybe he just has an early round and a championship round in him. That may not be enough as it is his only path to victory.