It's not about forger's profit. It's about secure system. In Nxt u need coins to generate block, more coins = more chances. It makes front-attack expensive: attacker'll need biggest part of coins to write buggy chain that still'd be most diff. one (all honest chains'll be forks in this case).

If u replace PoS with PoN in start, low amount of nodes'll make network extremly vulnerable. I'm not sure even with later replacement, cos node-based attack always'll be cheaper than $/bruteforce-based attack (buy coins to generate buggy chain or crack Curve to do the same or to kill project). Should we sacriface attack cost gap for "fairness" (equal node-based forging)? I'm almost sure, that correct answer is "NO".