Wrong. He loses UNRESTRICTED free agency. This means he becomes a restricted free agent after his fifth year. He is still, absolutely a free agent. He may negotiate with anyone he wants. Dallas has 2 benefits of this. Firstly, they can match any contract someone gives him. He is getting a record breaking deal from this, whether dallas matches it or not. Teams would be bidding against each other like mad, never has a RB this great hit the market this young. Secondly, they can tender a pick to him. The highest possible draft pick they can tender to Zeke is a first rounder, you cannot tender multiple picks to a restricted free agent.
Therefore, the only possible way Zeke is screwed out of this arrangement if he holds out of each of the next 2 training camps is if there isn't a single team in the NFL that feels a historically great RB, not even in the prime of his career yet, is not worth trading a 1 for. All 31 teams would have the opportunity for that deal. For 25 year old Zeke? You and I both know bad teams would be lining up to hand Dallas a 1 for him. So grats on the draft pick, but Zeke isn't going to have a problem holding out past the 6th.
Besides, this is doubly moot because unless relationships completely erode, you're liking franchising him after year 5 anyway.