I'm not f2p, but certainly not a whale either. I have a good number of valks and decently geared. Just got SSS Void Drifter with maxed core. Also just maxed out Ice Epyiphillium. One of the things I like about this game is that, for the most part, the difference in damage dealt by different units is more about how you play them than the unit itself.

That said I got lucky with Stygian Nymph and also pulled Path to Archeron. And she is so ridiculously stronger than anyone else that I find it hard to justify bringing someone else instead. Like the current event I tried using all bonus units but didn't manage to kill everything in time. Put in Stygian Nymph and I clear it with a minute left.

Not that I necessarily mind, I like the scythe play style. Umbral Rose was my early favorite unit to play (still waiting to pull Argent Knight).