I can see how this type of game that relies purely on good Gacha can be frustrating. Especially if someone is a collector at heart.
I played mobile games like Chain Chronicle, and Grand Sphere, where you have to spend tons of cash and hope for gacha. Eventually stopped playing those games after I understood just what type of cash trap it is (admittedly I wasted some money on those, so a lesson hard learned).

Games like Marvel Avangers Alliance on FB (though I dont like that one as I dislike Marvel Universe) is made in such a way that you spend cash on utility items like Refill Stamina, More raid points etc etc, but never on characters. All characters can be gained if you have team strong enough. Ofc if you miss and event - tough luck, hope for repeat in the future but still - the core of the game is - Everyone has the same fair chance of gaining All the characters in game, and the fights themselves are decided by how you combine them for all different types of strategies (going for burst damage ? Bleed damage ? Tank build ? and so on), rather than what DMM/Nutaku games present - where you have to spends thousands and thousands to complete your collection and where strategy means nothing when all you need is better rarity character to win. No brains, no tactics (with new girls being released almost every 2 weeks quite impossible).
So yes - I can see from where the disappointment/disgust/exhaustion is coming from for some people who stop playing.
Best way to enjoy this game is as a side dish. Go play some real game on Steam or Origin or whatever, beat few maps, slay some monster, shoot some zombies/players and then come back here, spend your few flower gems/stamina/manyus and go back to the first thing.
(ofc the first thing can be things other than games, like books, hobbies, work, etc. but you know what I mean.)