Don't underestimate the Western Hugbox, they have two countries that are almost equal to Byz in income and France by itself can match Byz numbers, never mind Spain and England. Also they are getting the colonial lands online that will be sending more and more money back into Western Europe and they have a clear expansion path into Africa for Spain. A move down the coast to visit Nutsoman in Mali and sieze province there as well. England can project force into the Scandanavian regions for additional pickups and France needs to munch more into the HRE area but they should be able to keep up and pass Byz in dev growth next session. As long as they can do that it favors the Western powers.
If Byzantium attacks Starnan then the Western Powers can reinforce, or they can take their piece of flesh as well and they should be able to take more by spreading AE over multiple countries (England, Spain, France and Holland)
Well, if you look at it from strictly on paper, numerical perspective, then yes, West is doing pretty well and has what it takes to beat down Byzantium with some help.
But on practice you have to take into account player behavior, showings and skill levels. The picture changes completely.