Hmmm. It's a shame it looks like so to you. The requirement to unlock weapons are based on testings made by myself with no rank cards used at all, so they're perfectly unlockable since I'm not good at all at playing with kb+mouse.
Apart from that, the price for the cards are high baically because they were made as a gift for our supporters. These supporters give their support every month to allow us develop the game. We didn't plan to release them as separate products, but we got people asking about that and so we decided to allow anyone to get it by just one payment. Also, they're there just to facilitate stuff for people. They're no mandatory at all.