The only person from WWE who successfully transitioned to UFC and won a title was Brock Lesnar, who was also on steroids. Brock got exposed against higher level competition and people his size or bigger. The skill ceiling is even higher now than in 2008, for instance if “Prime” Brock Lesnar fought now he would lose to every single heavyweight in top 15. The mountain is much higher to climb and I don’t think we will see WWE guys being able to transition, marking the death of the WWE to UFC Promotions.