I think the weight issue is a bigger problem with the MO3 than with the MO5.
I know that some will argue that a mini will work at 1330gms legal weight here in Australia,(unless rules have changed) and that it comes back to setup. I have seen mini's work well running at minimum weight and others that were impossible to drive. All comes back to smoothness and setup.
I have tried a light weight mini, however did not work for my driving style. At some tracks a light weight mini will not work due to having to much grip etc.
I wouldn't get excited about how runs what weight. It was just mentioned that a heavy mini can work as well as a lighter car, however there are pro's and cons with both setups.
Me, I will just run what works for me. Trying other setups just assists with getting a better handling mini for your driving style.
Good luck and Happy Racing.
Calvin.