Magneton isn't that reliable in the current metagame. It faces stiff competition as an Electric-type from the likes of Rotom-C (faster Scarf and Specs user) Jolteon (fast without a Scarf, letting it run LO / Specs to boost power) and Eelektross (slower Volt Switch and better over all type coverage for a tank in the current meta) and it has an unfavorable matchup against many of the more common threats in RU (Cobalion, Mega Steelix, Mega Camerupt, Delphox, and Houndoom are just some examples of rather common Pokemon that have few issues coming in and / or KOing Magneton) The two Megas I mentioned are undoubtedly the biggest problems for Magneton since they can take multiple Flash Cannons and are completely immune to Magneton's Electric moves. The other 3 common Electric-types I mentioned have ways around these two (Jolteon at least has HP Grass / Ice for neutral damage on both, Rotom-C has STAB Leaf Storm, and while Eel does struggle vs. Mega Camel, it does have Flamethrower and an EQ immunity vs. Mega Lix)