When you say things like "Very-short-term, they allow quants to make money on arbitrage.", it makes me think you really don't understand the role of market makers, proprietary traders, or quants.
Let me ask you a very basic question: why do market makers (the people you trade against when you buy or sell SPY) make money? They aren't stealing from you. They are providing you the service of liquidity. Market makers connect people who want to buy/sell now with people who want to buy/sell in the future. In the interim, they take on the risk of holding that position that you didn't want. On average, they are compensated for that risk.
The way you say "they allow quants to make money on arbitrage" implies that the quants are just "extracting money" from the markets without doing any good at all. This is the complete opposite of the truth, and more people need to understand this.
Let me ask you a very basic question: why do market makers (the people you trade against when you buy or sell SPY) make money? They aren't stealing from you. They are providing you the service of liquidity. Market makers connect people who want to buy/sell now with people who want to buy/sell in the future. In the interim, they take on the risk of holding that position that you didn't want. On average, they are compensated for that risk.
The way you say "they allow quants to make money on arbitrage" implies that the quants are just "extracting money" from the markets without doing any good at all. This is the complete opposite of the truth, and more people need to understand this.