I never said Diancie is shit you fucking faggot. I was just pointing out some of its flaws like Every Pokemon have.
Also, nice job calculating only physical attacks.
252+ SpA Heatran Flash Cannon vs. 0 HP / 0 SpD Mega Gardevoir: 222-264 (80.1 - 95.3%) -- guaranteed 2HKO
252+ SpA Heatran Flash Cannon vs. 0 HP / 0- SpD Mega Diancie: 592-700 (245.6 - 290.4%) -- guaranteed OHKO
Meanwhile, Mega Gardevoir has the chance to strike Heatran with a SE Focus Blast, with a chance to OHKO.
252 SpA Mega Gardevoir Focus Blast vs. 0 HP / 4 SpD Heatran: 296-350 (91.6 - 108.3%) -- 50% chance to OHKO>>23361005
Diancie can't fucking stall break, and stall-breaking is Mega Garde's best role.