Dragon Ball Super II: Orange Hillbilly Dooms World... Again.

[Yuki Akuma]

That's a good question. How in the Hell IS Gero' s droids better than the best of an entire universe that is dedicated to such things? Pretty sure that Cell at this point would be dying of laughter after seeing them.

I assume it's because Universe 7 has a much larger focus on combat than Universe 3 does.

It's also important to remember that Androids 17 and 18 are basically just humans with infinite stamina. They can improve like humans do, simply by training.