Weren't Vita's sales high enough, though, for the game not to bomb? Is it possible the Musou audience picked 3DS over Vita for some reason? And, if so, doesn't that mean Dyntasy Warriors Vs on 3DS could prove to be a big hit?
I think musou games rely on a big userbase, its not a system seller, rather people who already own the system would want to buy it. I don't think it'll sell systems and even if it did, I don't think people will buy the system at a high price, rather if its cheap enough they'll buy it for the game with other games in mind. Being a part of the a system launch means any additional hardware will sell additional copies of the game, its not just this game but all games that are a part of a system launches get affected in the same way. I don't think its a outright failure, as I said, low Vita sales definitely had an impact on it.
I think if 3DS or Vita had price parity musou fans would pick the Vita, but thats not reality. As lunch mentioned, SW is also a smaller game than DW. DW VS probably helped musou fans sway towards the 3DS also.
On another related note, long gone are the days where fans buy systems in hope for games that are in the far future, what matters the most is what games are out now and whats coming out in the immediate future. PS3 games like Trico, FFXIII/Versus and GT probably has helped this become reality, the slim came out before these games were out. They can buy a system when the games they want are out or is going to come out soon, and probably at a lower price. Its why MH had such an immediate effect on the 3DS and why the whole line up of the 3DS is helping the system stabilize at a high range, there is literally no need to buy a Vita right now.