Of course it is a loss.

The reason is that the backflow tickets are also depreciated. The backflow tickets are discounted sound waves combined with the anchor's return money, but there is still a loss.

At least 30% of the backflow tickets will be lost just to level up. Is this 30% appropriate?

There is a chance that the discounted sound waves will be banned. Generally, those who play backflow will change their accounts after playing once. They are all used by guilds. If you still expect this to upgrade, it is simply a way to ban the account.