How effectively can you mimic the stock market with spread betting

I’m maxing my Lisa then the remainder of my ISA both s&s

I’m In the 20% tax bracket working in tech so could end up in the 40% bracket in future? so would get more benefit from putting money in a SIPP then than now? Plus I want it accessible for me to buy a house in future.

I also supplement my income with value betting.

I heard spread betting is tax free so wondering if it could be an option to get a similar expected return and risk level to an index fund and if so how much work/time it would be to maintain?