You project is a nice one, its a shame to see your ideas clobbered like that. Maybe there is still some room for you.
There is some differences that you can exploit. Especially if you are making a standalone, not a shield.
The 328 can do 20MIPS throughput. whereas the 32U4 is only 16MIPS, even have the crystal removable/switchable and then people can select an external clock.
Seems the 328 has 4 less instructions, whatever they are.
Plus many other differences...
If you are still / were considering a big screen project, I'm working on a library for a 3.2" on a mega 2560 that could help you achieve a nice result. My goal for the library is to actually make a game out of it.
Either way, I'm sure there is something your platform could incorporate that will elevate it well above the performance of the esplora. They may have gotten theirs out first, but this also means you can 'esplore' it and create a better system.