This would make to an interesting battle but sadly...

Unicorn Twilight would not win.

It's just the matter that she got far was because she was an alicorn in this battle.

The only reason that the Princesses gave her their magic was because she was unknown to be a new alicorn.

A normal pony would not be able to hold THAT much alicorn magic.



Really great imagination, but sadly, the way things are... Alicorn magic just makes sense in this scenario.