5 ults, same exact time, i think it's pretty op.
I played against, it's not that op if your team is smart enough to build zhonyas.
The 5 ults are more annoying if they don't occur at once, and when that happens it's pretty easy to avoid it. Also, I don't think you can ult at the exact same time, I don't recall that happening at all, think it's one at a time.