How about King's Raid? Pretty grindy after you reach past the 60s, but it's F2P friendly. If you don't mind spending a little bit of cash, the daily rubies is a pretty good deal. It's still fairly new (several months) and I can see a lot of potential for the game if the devs do it right. Would recommend Grandblue Fantasy as well, but the grind is real, just a heads up for you. Wouldn't recommend Age of Ishtaria though. I played it competitively for a year or so, and from what I've seen it's quite P2W, especially if you're aiming for event rewards.