Personally, I make every effort to write in presentable English
here, though I sometimes allow some typos to slip through.
But as for your concern about the command of written English here
and in Singapore generally, I'd say like most would say; " Where
got time, lah! You can read, I can read, can oredi lah!"
As illustrated, writing in proper ( or presentable ) English takes
effort, which is basically practice, and habit.
The ability to switch between the two, English and Singlish, is key
to this particular issue at hand.