Co-op TD is my style, but the quests are a bummer..

XD Hero and Co-op Tower Defense, both fun games that are my style, but it's a shame they all turn into 500 gems after one quest ㅠ Some games maintain or even increase their value, while others drop moderately, but this is just too disappointing.. Lately, dealers were important early in this game, but now it seems like supports are more important. Should I buy it with gems since only the same 'First Demon God' keeps coming up... They say gacha is more efficient in the long run. Anyway, the quests are disappointing.. ㅠ