Intellectually I know it is probably better to focus on a few things.

It's not about it. You're using steemit as a social media platform. If you want to mix subjects then it's best to open 2 different accounts. Otherwise you will be losing interest coming from your followers. That's just the way it is.

It's better to post 1-2 posts a weeks and engage with your audience. Dont worry about not writting much. Just focus on something, make sure that your followers have similar passions and carry on.

Mixing many topics will not get you far.