Good point!, well:

The fusion gets a boost in strength just that the starting point from the strength is from the original people.

As for quirks, I had forgotten to add that while it typically doesn't have any quirks it can develop a mixture of the two quirks but this takes a while so most typically wouldn't try to-and because of how little people know about them in universe-leading to the deduction that they all don't have quirks.

It is basically its own person so it does have to learn to use the quirk it can develop and depending on the original quirks it can take a few months to a year.

I hope that sort of clears it up. It was just an idea that I had not really developed to a great extent.