The RS-25's notoriously slow, expensive turnaround was blamed on its complexity. The Raptor appears about as complex.
Both use regenerative cooling.
Both use preburners to drive turbopumps.
While the Raptor has no need for the low pressure pumps, it does run at a much higher pressure.
While the Raptor does not need the seal between LOX pump and turbine, it does have a chemically active flow of hot oxygen coming from the LOX preburner.
While Raptor does not have embrittlement from hot hydrogen, hydrocarbon fuels tend to burn hotter.
Why does the SSME require several months for turnaround, whereas the Raptor needs no time at all?