James Gunn has stated that he would not re-cast Drax. Either way, by locking this property into the Guardians of the Galaxy, they've concluded that it will be the current makeup of the Guardians that will be featured in the attraction. I don't see what that's a problem.
Having said that, if I also suggested that you can build a Wakanda land without T'Challa, people would also say what's the point? There's no definitive answer to how best to represent an IP. Disney had the original Star Tours exist for decades without any of the prominent characters from the original trilogy, and then they built Indiana Jones Adventure in Disneyland with multiple Harrison Ford animatronics.