Ehm, yea, it's beatable by using a auto clicker. It still took for ever - i really don't want to imagine how my fingers would hurt if i clicked by myself. A few suggestions when the game should become playable without an auto clicker:
- one raider takes it all? really? maybe take of 10*wave^2 (at the beginning = 10*1*1 = 10, before the final boss = 10*5*5 = 250)
- don't double the cost for the next level each time. I ended up with costs of 5.000 metal or 10.000 wood. Even with the auto clicker and an almost perfect game i couldn't afford the 8th damage and 9th ward upgrade (not sure about the number of level though)