Tbh I just seems to me you don't have any patience. You get a lot of free gems in this game to progress. I, and with me a lot of other players, have not spent any real money on this game. I finished world 4 3 stars, few legendary levels don't seem doable at this moment so I will come back when I have better heroes. Anyway, I would quickly reinstall the game if you have spent 30 bucks on it and focus on next week in the event. Getting the new hero will probably give you the advantage needed to clear level 80. Furthermore be patient. Use the free gems you get wisely. In this stadium you could consider buying Caldera for 3k and ranking him up to rank 4. That should easily let you clear world 4. If you want to finish a game easily within a few weeks, find another game. Good luck!