Solo play has been simple so far, right now there are plenty of people looking for groups for the event battles so it was easy to just hop in one. But I was also able to solo.
This is a F2P game in Korea, so grinding is the name of the game. Can't beat it yet, go grind a bit more. Most classes can solo, it may take a while to beat a boss/event but you can do it if you know how to play your class.
I've been a Slayer which is DPS and it has been fun to dash in get a couple powerful hits in, dance around the monster till it is vulnerable and get a couple more in. I think one boss took me 6min but felt like 30seconds