I used a really similar team concept in POs UU about a month back, but it used an offensive core of just Scarf Victini and LO Roserade (I generally stick to balanced playstyles as opposed to all out offense). It's such a great strategy to score easy kills, and you're executing it perfectly here.
About the team, it looks particularly vulnerable to SubCM Raikou sweeps. Darmanitan won't be there forever considering Donphan doesn't Spin nearly as reliably as it did in Gen 4. Once he's gone both your other checks are 1-2hko'd by unboosted super-effective Hidden Powers. It also has enough space to set up (Zapdos, Froslass, -2 Roserade). Granted, chances are against most teams you're probably able to keep the offensive pressure at a high enough level that this isn't an issue, but against well built balanced teams aiming to get a Raikou sweep (say Donphan / Roserade / Slowbro / Mismagius / Snorlax / Raikou), you might have some trouble.
My suggestion is to try to find something that can actually beat Alakazam and Raikou and use it over Zapdos (who seems to contribute the least to the team). The first thing that pops into my head is Bronzong, but unfortunately that's not UU here. I'd say use Registeel, but then you're trading the Ground immunity that Zapdos gives you for another Ground weakness. I'm not really too sure what you can do about it at this point, and you know Smogon's UU better than I do, so I'll leave you to figure it out.
Also, 152 HP / 252 SAtk / 104 Spd Modest gives Roserade a 299 HP for LO and enough Speed to beat Adamant Honchkrow. This is the spread (with a bit more Speed over SAtk to beat things like defensive Zapdos) I used on the team I mentioned earlier and I never once missed the Speed.
Anyway, I'm probably rambling at this point so I'll just say nice team, congrats on the peak and good luck in the future.