I don’t agree. Maybe it was at the beginning. At this point, the micro structure is probably closer to forex with liquidity providers taking the other side of retail order flow.
Well is it possible to swing trade BTC? If so, then it should be possible to day trade, the difference being the trading fees: are you able to overcome trading fees on shorter time frames? There are algorithms that will make profit on any time frame, but the shorter the time frame the more you have to pay attention to the cost of trading. What markets do you believe it is possible to day trade? Ok, what is the Average True Range per 24 hours for that market? If BTC is the same ATR or more, then you should be able to trade that too, since it comes down to how much volatility is available versus trading costs. Trading costs, if using market orders, make my own algorithm effective on time frames four hours or more with a trade happening about one per four times frames, so about 1.5 trades in 24 hours. The question you should ask your friend is what is the ratio of trading costs to profits, besides how many times a day is "day trading". In theory, you could actually pay out $100 for every $100 of net profit ($200 gross - $100 cost) and have a business, if your algorithm is reliable enough.
nothing preventing a retail person from creating an exchange, a token, becoming a liquidity provider, taking advantage of the fragility of what's in place, ...