Apple came out of nowhere and invented the smartphone because the existing system was controlled by the telcos and horrible phone technology. The same thing can easily happen again.
It makes no sense to limit Netflix on phones and people would probably stop buying iPhones.
If the EU wants an "open" phone ecosystem, they should foster real innovation in their space and build it themselves.
Furthermore, if we lived in a world where the two main OS's were locked down to an insane degree, we would also have plenty of alternative operating systems. The reason we don't today is because we don't really have a need for it, in the same way linux has a monopoly on servers and nobody really cares.
Those make up 0% of the market [1], which classifies Apple and Google as gatekeepers.
[1] https://gs.statcounter.com/os-market-share/mobile/europe/
If you have a market with a handful of companies producing good products, and a handful of companies producing shit products nobody wants or buys, you cannot claim that the companies producing the good products are "gatekeeping", and that's the reason why nobody buys the shit products.
It doesn't matter how they became gatekeepers.