The only thing that can mess up Djokovic is himself or an injury. He is so good on grass that he dosent even need tournaments before to get use to the grass. He isnt playing anything before Wimbledon and he always does this and dominates everyone. Tsitsipas is bad on grass this season and i dont think he will make it to the semis even.
I didn't know that he also didn't play any prep tournaments for Wimbledon in the past. But I think that anyway he is taking care of his body and choosing tournaments wisely. I would even say that for him it is all about the four GS year round. He knows that if he "only" wins those GS tournaments and has just a few other tournaments with decent finishes, he will even stay at the top of the ranking. He wants his body to be as healthy as possible for the GS tournaments and I believe we will see him playing for maybe three or four years. I said two years before, but when I see him playing I couldn't come up with a reason why he should stop in 1.5 years from now.