Bound by a non-compete, and offers to work at a competitor startup

So, from an investor's POV: if you took money, you are committing to work on that startup full time. If you start something new without shutting down and discontinuing the old thing, I could see myself being annoyed at being kicked out of what is essentially a pivot, since you embody most of the value of the invested startup. They invested the money, you invest yourself.

However, I feel that it is unreasonable to expect ROI from the founder shutting down the company and taking a job (even if it is in the same space.

You have to make sure your investors are taken care of, especially since you wrote the following...

"In fact this new company is kinda a branch of my old company is going to be considered a competitor."

If you become an employee of the company that is acquiring you, your investors might accept that, but otherwise they are technically in business with you. Your new business sounds an awful lot like a pivot.

One takeaway from this is to have a machine for non-company stuff, and use it--there's really no excuse these days.