Ya, Yanmega Magnezone is much better than Stage 1s even though Donphan hits Magnezone for weakness. Its not like Donphan has a type advantage over the entire deck. Yanmega's resistance helps, and Kingdra helps too. Against Stage 1s, save your Magnezone for Zoroark and Yanmega, and use Yanmega for Donphan, and you'll be fine.