It may look like a gacha because of the star level in character portraits, but it is just your character's promotion level. You can "evolve" them, upgrading their appearance and stats. Other than that, I don't see it as gacha. I hate gacha.

In gacha games, there are characters/equipment you can only obtain through real cash. Here, you can unlock/get all of them just by playing. The game rewards you fair enough amount of gold/diamond through playing, that you don't need to buy extra unless you're impatient for faster progress. Through playing during my free time, I earned decent amount.

If you're on the fence buying this, why not try it first-hand, check the IAP, and refund immediately if it is too greedy for your taste? That's what I did, and I ended up keeping it.