I've been thinking about why Mecha Freezer did not even train a bit to be multiple times stronger than Goku SSJ (Namek), instead of being slightly superior?
The answer according to my theory is the following, it may be that the robotized state has increased a certain amount of its power, but it prevents him from training or having the body prodigy to increase his power in that extraordinary way.
I don't think this is what happened. Mecha and Cold were completely oblivious of Mecha's real power as can be seen by his reactions after Trunks kills Freezer, which means that they didn't check what was possible for mecha or not.
The reason Mecha didn't train is because he was aware that SSJ Goku beat him while he was in a very injured and weakened state, and knowing Freezer, once he felt healed he probably rushed to the earth to kill everyone. Furthermore, his mechanical implants improved his low stamina which is something he could perceive, so he assumed he was more than ready to fight the saiyans.
Also it should not be forgotten that Cell has Mecha Freezer cells and not normal Freezer, therefore, Cell does not have a prodigy body to have the same Freezer gains.
Cell had Freezer's Cell's, not "mecha freezer" cells, because there are not "mecha freezer" cells. It's the same body but with the 75% of it replaced by mechanical implants, but the Cells that remain the other 25% are pure, 100% normal Freezer cells.
Furthermore, the zenkai Cell had before dying proves that his limit of power was the same as Freezer's. So, even if Cell couldn't do the Golden transformation, his power should be at the very minimum as extraordinarily high as Freezer's.