The people that developed Wayland were the exact same people that developed X.Org. I'm sure they thought of all possible options because they are actually very smart people.
Well: 1) it isn't always the case that the people who develop a system in the center of an ecosystem are actually the people who know best how the entire ecosystem should work (and in fact there is an entire trope of second system effect destroying such a reboot); 2) it isn't at all obvious to me (and in fact it feels incredible to me) that the people who put most of the effort into X.Org decades ago are actually "the exact same people" who are in charge of maintaining it today; and 3) the specific thing we are talking about here has been discussed numerous times in the past decade by people developing low-latency and high-performance apps--such as games, which is where you really want to be able to get the display server out of the way--and was, in fact, known to introduce a ton of latency that they were going to figure out how to fix some day (a similar situation to how Wayland completely fucked up display scaling by forcing integer scaling, which required patching later and now is a wart in the architecture already).