Pay to win: Yes
Can you still achieve end game status w/o a single cent: Yes, but I hope you have a crap ton of time and great friends to aid you along this 5 year plan.
As for Chapter V, new race and new classes coming out in a little more than a week.
Champions and Warlocks. They're very OPed...
Example: Warlock/Rogue - 5,160 raw dark damage with "Crime and Punishment" and CD is only 4 seconds
Champions - 80% str converted to stamina, +112.5% pdef buff, a skill that gives instant aggro, a skill that instantly restores hp to max, a skill that is spammeable until rage runs out
That is however, to be expected. If they weren't OP, why would people reroll? Why people buy puris, repair hammers, plussing jewels all over again?

After a while, they'll be toned down again because of epic QQing on the forums over their skills.