I put this in the comments so thought I'd paste it here too.
I've been playing since softlaunch and I'm in one of the top ranked guilds. There is only 1 real IAP currency which you do get during explorations and for achievements anyway and are not needed. But of course people can buy their way to the top via this system as in all these games, but eventually you'll catch up.
It's a very good game with amazing graphics, defence can be well thought out and planned which makes a huge difference. You units actually have skill trees that improve stats and also give some active/passive abilities which I really like. The only thing that's missing for me are heroes but they did hint at legendary pirates which I thought we would see before global launch.
Although we have been stuck at pirate hall 6 waiting for an update for a while before we could do more so I've just been auto collecting for a while.