I'm from Singapore originally so I think I'm qualified to comment!

In short, yes Singapore English really IS that bad!

However, the educated Singaporeans are fully capable of holding conversations with foreigners in PERFECT English. And their written English is often better than "native" speakers (Brits/Americans). It's just that when they speak in Singlish, no-one can understand them at all. It's like when Jamaicans speak their local "dialect". It's incomprehensible.

Singlish is made up of different sentence structures, borrowing from Chinese (both Mandarin and dialects) and Malay.

The trouble is a lot of the local working class Singaporeans can neither speak proper English nor proper Mandarin, they can ONLY speak Singlish! This is particularly true for those who are educated only up to secondary level i.e. 10th grade in the US.