I can't comment on US market but our market in OZ and the Dax I haven't found this to be a problem. Sure a point or two here and there but it tends to even out in the end. I know our market if the cash gets out of line with futures it gets arbed away pretty quick.
Yeah, but it doesn’t. Index arb/program trading is persistent as the barrier to entry is high and dominated by Virtu, etc. There is no reason to run the TA on cash other than granularity (penny “ticks”) but it’s not executable as the synthetic is not as liquid and the microstructure is poor. And ofc the cash synthetic is going to follow futures but the cash index print will not.
