I would think any Mandarin speaker knows exactly how to pronounce Pinyin, because the correct Chinese pronunciation is the correct Pinyin pronunciation. If you’re talking about reading and understanding pinyin, though, I can see your point, but the Pinyin is just there to represent the Chinese, not provide another, different pronunciation of the Chinese.
Wanna hear something hopelessly geeky? Sure you do…
Although Esperantists normally use Hanyu Pinyin (perhaps because China boasts tens of thousands of Esperantists, thanks to flirting with that language during the Cultural Revolution), a few adaptations have become widespread. The same way London becomes Londres in French, or Koeln becomes Cologne in English? So Esperanto (in which nouns end in -o) has words like
Pekino (pay-KEY-no)
Tajvano (tie-VA-no)
Tajpejo (tie-PAY-oh)
Am I the only one who thinks that the Chinese should be changed to match the romanisation? Try saying “Taibei rocks!” Chinese style versus “TaiPEI Rocks”. The problem solves itself.
Taibei when speaking Mandarin, Taipei when speaking English, Taipei written English…
Which button do I click? 
