I don't think it's fair to critique it just because its original intent was as an auxiliary language. I would argue that intent failed. But it has native speakers, and it has communities who use it, and that itself justifies a language's existence.
The point of Esperanto wasn't just to be a shared language. Much more importantly to Zamenhof and early Esperantists, the point was a language that wasn't bound to provincial, ethnic, or religious identity. This backfired in the early 20th century as Esperanto became associated with, e.g., Jewish and Anarchist groups. But it seems like in the latter 20th century Esperanto reverted to an internationalist language without association to any distinct political movement. And in that sense it's once again a reprieve from and perhaps an antidote to provincial power dynamics, notwithstanding its European language bias.
I also haven't seen any of the other conlangs demonstrate they can be both as expressive and easy to master.