Power up Magneton ?

Have you got an Arcanine or a Jolteon with good moveset? Training a gym against a Lapras is terrible but destroying a gym held by Laprases is easy man.

Don't power up a magneton with bad IV.

I have a few with Spark and Discharge and they perform really bad imo. Never tried one with Flash Cannon tho.

Best option to counter Lapras is still Arcanine.

Magneton works well, but you will need to dodge - it really is fragile. My preferred moveset is Spark/Flash Cannon but even magnetbomb works. Does okay against Charizard too.

I haven't used mine much of late though - a powered up Jolteon does the job more quickly.

Dont power Magneton up. Stats are medium, attacks are bad.
Gyarados, Jolteon and Arcanine are the best option against Lapras. Vaporeon and Slowbro with Watergun/Psy are decent option too.

I use Magneton with Discharge against Lapras. I currently have it up to CP 1639, still rising. However, I do this is just for entertainment purposes; it is not stardust-efficient at all. Over a complete charge cycle, Magneton with Discharge deals about 20% less damage than Jolteon with Thunderbolt or Thunder. This is balanced by taking 20% less damage from ice and dragon attacks. Thus, only against special opponents Magneton will do about as good as a common general-purpose electric attacker like Jolteon.

Max this metal pokemon up! Maybe in Gen 2 or 3 steel will get buffed