Xur needs to sell more exotics, not less. The issue isn't that they are too easy to come by; it's that they are too hard to come by. You can only equip one at a time so more selection will cause them to be more diverse. The problem is that they are so hard to come by that when Xur sells one a large portion of the community is using it all-at-once because their access to exotics are so limited at any other time. If exotics were more available then the ones used would be more varied as people started to gravitate to the one that they actually enjoyed playing with based on personal preference, rather than just using the only one that they actually owned.