I realize the numbers are purposely under-tuned right now, but even considering that I think that the design of this espec is not very well thought out. I'd like to preface that I am not talking about aesthetics or theme, but purely how it performs in a practical sense.
Core Mesmer sustain is balanced around its passive defense with clones providing the ability to misdirect/block enemy attacks in the heat of combat, and active defense cooldowns (distortion). When you take these away, Virtuoso has nothing left to sustain itself, and provides nothing substantial in return. After playing with/against Virtuoso last night, I found that it's just free farm in competitive play at its current state.
I think it's particularly problematic that the new F4 are channeled. Mesmer relies on its F4 to buy time to turn around an unfavorable situation (because it needs time to ramp up its burst). Virtuoso doesn't have that luxury, so at best you're just prolonging your opponents' offensive window, with no opportunity for follow up of your own (unless you can burn another CD like stealth or blink).
In order for Bladesongs to work in their current form, they need to be immune to reflects, and lose their cast times. It doesn't feel nice or rewarding to lose a whole stack of blades, because they are extremely telegraphed, and losing the unpredictable/instant nature of core shatter provides nothing in return right now.
tl;dr I cannot think of a single situation where one would be better off playing Virtuoso over any other Mesmer build except for memes.
And of course, this is from a PvP/WvW perspective, because PvE balance is w/e.