At peak (December 2017 to February 2018), my small python bot was making between 500 to a couple thousands dollars per day. It was even possible to do arbitrage by hand at that time since you sometimes had a 10-20% difference between the markets.
Can confirm. Early January 2018 I made $10k in a week because the BTC/JPY price was 10% higher than the BTC/USD price. It required a partner in Japan and lots of international money remittances though...