TGMD - solid team, and thanks for owning the Dark Horse challenge with it ;)
The fact that you depend on Sand Rush Stoutland and Ice Shard from Mamoswine to revenge-kill many threats, it's understandable that QD Volcarona and RPolish Genesect can have its way with this team. There's an easy solution that I like to suggest frequent on specially-defensive Rotom-W: Thunder Wave > Will-O-Wisp. T-Wave just makes sense, when you consider that mons that Rotom-W is supposed to stop - speedy special sweepers! Paralyzing QD Volcarona and RP Genesect would instantly ruin their sweep.
It seems like you're experimenting with your Latias spread; may I suggest 132 HP / 124 SpA / 252 Spe? This allows you to OHKO Keldeo after SR / sand damage (88.7% of the time ;x). Even Max HP Venusuar is OHKOed by Psyshock after SR damage. You have the Speed to check dangerous threats like Thundurus-T, Keldeo, and Terrakion. Even more, you still got dat bulk! You wont be 2-shotting Blissey after sand & SR did with your Modest Latias, but you really need the Speed. Even with the current spread you can 2HKO Blissey coming in at 82% (with SR + sand), so that's plenty of pressure imo.
Thanks for sharing your team, The Great Mighty Doom!