I always felt like the SpO2 feature was mostly useful for those worried about covid affecting their blood oxygen levels, and it came out a little late in the game for that purpose. I have one of the fingertip SpO2 devices, and rarely use either. When I have had covid, it never dropped below 95%, and my personal normal range seems to be 95-98%. My current S8 was sold before the feature was removed, but I use it very rarely, and probably wouldn't miss it at all if it were gone.
My read on the whole situation is that Masimo likely wants to hurt Apple enough to extort some sort of licensing deal from them, but Apple is pretty stubborn when it comes to those tactics. I don't blame Apple for that - once you open the floodgates, watch out!
The claims that Apple "stole" the tech are baseless and absurd, as Masimo was unable to convince a jury or any judges of such. They ran to the regulators at the ITC, who are less informed about the relevant patent laws, and convinced them to enact an import ban based on who knows what arguments.