I'm pretty sure you spent money to enjoy or u just hate grinding, I reached KOG 6 times in a row without spending any penny on the game and I'm planning to get that 10 KOG icon soon!
First KOG (April) = ancient gears (my favorite deck of all time, I have 5 Prismatic ancient gears monsters).
2nd KOG (may) = ancient gears
3rd KOG (june) = anti trap, ancient gears, unga bunga last gamble
4th KOG (July) = Sylvans (post nerf)
5th KOG (August) = 5 duels furhire + Sylvans
6th KOG (September) = Koa'ki Meiru
If you don't have Koa'ki Meiru cards don't go into gaia Genesis just for it, the deck is very inconsistent and bricky, you can find my build on page 2 with some instructions to use the deck optimally, the meta is shifting now so I don't know, I realized Amazoness and fur-hire are vanishing so you can use Koa'ki Meiru Boulder easily together with winged kuriboh, drowning mirror is becoming useless.
That's my mentality when I just started the game and been playing for 3-6 months. A year later,what I realized, is the scarcity of resources. lvl 45 characters, scarce gem incomes, and waiting forever for decent events, this is the bigger picture for all players, and the final demise of f2ps. Scraping every month or two to get one meta deck, repeat and rinse. Game is free, YOUR TIME IS NOT.