1. Ever heard of diminishing return? It's every where. The first X is free/easy, but if you want more, you gotta pay up. In this game, you will see this in magatama, 8 gate, cave rune etc. Why would you ever get more keys if 2 lv 2 runes produce a lv3 that's less than 1.5x of a single one?

2. top 50

Also, your point #1 and #2 conflict with each other. As you said, only top player can plunder and fact of the matter is, only the topmost player will succeed reliably. How do you become such a player? Ptw will help!. So in a way, spending money is like an investment and plunder is the return on investment.

Granted, ftp can be strong enough to plunder too. I could, I don't but I could, easily plunder and I'm ftp. But it's less reliable and heavily depends on the server demographics.

So while I dislike plunder, your reasoning doesn't hold much water.