105 speed is not that good anymore, and losing 10 points upon evolving is just too much. Base speed under 100 hurts a lot, and Mega-Garchomp is proof of that
Also while the coverage is great, most moves are pretty low-power.
In order to fix it, this post
>>21204379nails it
Though I'd also suggest maybe Close Combat (since it turns into a Fightning type) and a better STAB Move. Maybe an event Elekid with Bolt Strike or something. Or Volt Tackle. I don't know
