Magneton- UU D-dance Altaria counter

So, I decided to formulate an Altaria counter today, so this is what I came up with
Magneton W/Leftovers
EVs: 255 sp.atk, 255 defense
Nature: Modest
Ability: Magnet pull (for more than just altaria)
Moves:
Tri attack
Thunderbolt
Explosion
Psych up
The main strategy against altaria is to attack with with Tri-attack and T-bolt, then use psych up after it D-dances one or twice, then explode on it to kill.

It seems like you belive Magnet Pull traps everything, but it actually doesn't and therefore Altaria can just switch.
Pretty much every DD Altaria has EQ also, so Magneton in general will not work as a counter.
Investing 252 into HP into most things (Magneton included, there are some exceptions regarding base stats and such) actually increasing physical survivability more than 252 Defense does as well as Special Defense (which helps make better use of his Electric, Ice, etc... resistances).

Psych up is just a bad strategy if you are going to explode... What's tge difference between what you are doing and having a max attack Magneton with a Choice Band attached to it so it can Explode on Altaria?

The best way to "check" Altaria with Magneton is run a Timid set with enough EVs to outrun a +1 Adamant 252 Speed Altaria (244 Speed EVs) and give Mag a Scarf and HP [Ice]. You will most likely need SR to secure the OHKO, but that shouldn't be a problem.