You should not assume your password manager is unhackable.
That’s my main point. Perfect is an enemy of good indeed, but I feel that doing things properly the first time is a good idea in general, especially when it as easy as using a different app for your TOTP tokens. It’s a low hanging fruit really.
It is reasonable yet subpar under a threat model where you do not trust any single provider, which is a model I find appropriate most of the time.