Yeah it's a gachapon game, but Opera Omnia is probably the best and most free-to-play friendly. There's only a stamina meter for a very specific dungeon type, so you can just blast through the entire campaign at your own pace and do whatever you want. There's also some really interesting hard content that can be a lot of fun figuring your way through.
It definitely has some gacha-related problems like RNG really boning you if you want something specific and some unusual power creep (it does allow for like every character to become useful depending on the situation though). The multiplayer is a lot of fun, but does have some issues around speed being more important than just clearing it (somewhat fixed with the token system used more recently). The multiplayer event rewards give you tons of stuff for just playing it.
If you want to add me my code is: 619 346 175