These days a naive market making strategy in crypto just incinerates capital very reliably as the tiny bid ask spread is a small fraction of the adverse selection risk (whole spread moving past). They did probably make money on this in the early days and got smoked when the sophisticated tradfi players joined.
Front running large trades by looking at non public info on the order book is possible but this is also fraud, so not a strategy to avoid legal troubles, and it also only works if the large traders are naive and not adversarial (putting fake large orders to front run you etc).
What SBF could have done is close down Alameda when it was clear they were not competitive, and concentrate on growing the exchange by reinvesting the fees, but that would have clipped the growth and donations/acquisitions lifestyle to something much less flamboyant.