I don't know enough about Esperanto to gainsay you, but I would say that your objections would apply to any constructed international language. The only alternative would be for a language to be imposed through some sort of imperialism. Even that leads to variants that border on mutual unintelligibility. One of my job responsibilities is to copy-edit engineering reports, some of which are generated by native Mandarin speakers and passed to Indians (some of whom are from a Hindi-speaking area and some from a Tamil-speaking area) before they get to me. I get some interesting samples from time to time. As to inflexibility I would guess that there are likely many words in modern Esperanto that were coined since the time of its invention by Zamenhof. This would be more a function of the number of people who are using it in a day-to-day manner than due to its nature as a constructed language.
