Earlier quoted context omitted.
'Perfectly fine' definitely doesn't mean 'usable' in my dictionary. But I see that perhaps the parent didn't mean to say that the web version can do everything the app does, so I have edited my comment to be less confrontational. Thanks.
Right. OP here, FWIW, in my colloquial English (right or wrong:) "Perfect" is, well, perfect; does everything I want and cannot be meaningfully improved. "Perfectly Fine" on the other hand, the key word is "fine". It is "eh. It mostly does the job. I cannot begrudge it too much. I have bigger things to rant about. It's perfectly fine." "Fine" is like "Nice". It's fine. It's nice. Note quite "Good", let alone "Amazing…
(I’m not a native speaker.)