I’ve certainly had the experience of not being able to guess the nationality of another Esperanto speaker (and also had people not correctly guess my nationality). On the other hand, I’ve also encountered people who still had an easily identifiable accent, even when they spoke Esperanto with great fluency. Duncan Charters has regaled party-goers for decades with his “round the world in Esperantujo” routine in which he seamlessly passes from one country’s phonological peculiarities to the next.

Also, I think there’s great validity in Claude Piron’s criticism of the “Okcidenta Dialekto,” i.e. the tendency of English-speakers and Western Europeans generally to use word-roots taken from their own languages (generally often Greek and Latin roots), instead of using the word-building facility Zamenhof built into the language to create a clear concept using basic Esperanto roots. It just makes it that much harder for people whose mother tongues are linguistically remote from Western languages to learn Esperanto, such as Asians.