Stable coins are going to be hugely profitable like you mentioned due to the various arbitrage opportunites but also all the transactions that will happen allowing people to make real world purchases without worrying about value too much. It also helps maintain funds in crypto and keep the market stable.
The ideal situation is not even to take your money out of crypto and simply use that for every day use one day so we dont need banking services and have to deal with tax. We can earn and trade in value just as we feel like, thats the dream