I know, and I guess many of you, few people who are good at both. And we know if from their works. To put a rest to people advising you to choose one - you've to show to them that you're good with both. Once you do that, no-one is going to ask you to pick one.

If your boss and/or friends advised you after seeing your work, I'm sure they've a reason.

Are you really that good with both or 'just' good doing both?

In any case, you'll be a good (co)founder for sure but you might not be a good employee.