See my posts on last few pages in this thread about how XP works: https://pokemonrevolution.net/forum/viewtopic.php?t=18683&start=90
Short version is that Xp is proportional to the first base XP yield listed on Bulbapedia. So Magnemite is 89, Magneton is 161 and Magnezone is 211. Magneton takes 1.81x more XP and Magnezone takes 2.37x more XP to level compared to Magnemite.
On the plus side, if you teach a magikarp bounce and EV train it, you can level it to 99 really fast because its base XP yield is only 20.
Don't get me wrong, I understand the premise now. I'm just disappointed with it. :Sleeping: