Having two megas isn't a must, in fact, most teams work better with only one.
While his team isn't weak to Intimidate at all, it is still everywhere in VGC, and Bisharp can do massive damage at +1 with LO (as he stated). Also, this is probably just me, but I will never ever consider using a M-Kangaskhan in my entire motherfucking life (in VGC, at least), unless it gets nerfed or something on ORAS / a future gen. Mega-Kangaskhan is for pussies and that's it.
As for your team, the synergy is pretty okay, I like it, however there are two things I would suggest changing:
- on M-Manectric I would run HP Ice over Overheat or Thunderbolt. The extra Thunderbolt damage is often unnecessary and most of the times volt switching out would be better than staying in. Overheat is kinda useless as well as it only helps you damage a few things harder, such as Aegislash, Amoonguss and M-Mawile. HP Ice, however, helps you deal with dragons (specifically Garchomp and Salamence which can hurt your team pretty badly) and ground-types in general.
- M-Venusaur is also quite threatening to your team. Ferrothorn is the only one who can tank hits from it, and Bisharp/Specs Hydreigon are the only ones who can hurt it (Bisharp not much tho, since most spreads run tons of defensive EVs and they usually carry synthesis). Not to mention that it's very often paired with Rotom-H since it can help the former deal with Bisharp and Ferrothorn. That said, If I were you, I'd somehow try to fit Talonflame in your team (would replace with Clefable, or Hydreigon if you're that keen on keeping it). Talonflame has great synergy with most of your mons. It forms a Fire/Grass/Water core with Ferrothorn and Rotom-W, not to mention that Tailwind (if you happen to run a LO set over the common CB set) helps Bisharp, Rotom and Hydreigon a lot. Taunt also makes it an excellent partner to Bisharp. Also, before Mega, Manectric has Lightningrod to draw away electric-type moves completely, so mons like Raichu become rather easy to deal with. I don't want to change your team completely, but I just feel like the addition of Talonflame to it, be it banded or lo'd, would be great.
Besides this, I agree with everything else you stated, i.e. leads, ev spreads, etc.