She IS a nuker, an assassin - just look how much damage your RQW combo is. It can kill a lot of people, and it can be cast quite frequently due to her low cooldowns.
She's also got a great chasing/escaping tool due to versatility of her ultimate.
The reason why you still can't see her very often is because:
1, she gets quite boring rather quickly (which is relative, so don't take it personally if you main her - I'm speaking in general)
2, the lack of strong AoE spells, which is more important in the competitive era where the outcome of a match usually depends on team fights and not on whose team is more fed.
She's a great ELO-raiser and may be the ticket out of the so-called "ELO Hell" for a lot of people (according to a few professionals), but once again, her kit just doesn't fit my playstyle.