The reason, in my mind, that MK has a bigger attendance then DL is simple. WDW is a bigger resort and has much more to offer therefore it has more people coming to it. So, yes, in that respect DL would have a bigger draw in WDW then it currently does. "The blessing of size". If it were in WDW the same size that it is now, it would have to limit attendance due to being smaller in space and evacuation requirements would create a limit to the number of people in there all at once.
I went to DL once and it wasn't even "in season"... end of September. And I found it stifling due to the size of it. Yes, they had more attractions, but, getting from one to the other just seemed like a huge chore. I found the "locals" were snobbish and cultish, that wouldn't happen in WDW because of it's diversity due to size and location.
To answer the question... DL at WDW would, simply, by the numbers have higher attendance, but, unless it was given the same space as MK, it wouldn't ever get to have the same exact attendance.