That's certainly not the case here, even if it's true sometimes. The duopoly is gradually tightening their grip on the customers' wallets. It's worth it at any stage to reverse their cash grab.
This is bound to fail unless they get the full stack and even then, it will be for specific phone models, x86 is an anomaly in having a cloning freedom that IBM did not intended.
Open firmware is but one part of the equation. The evolutionary pressure of state actors trying to deploy malware on iOS and Android forces those platforms to develop vulnerability mitigations and security architectures that currently just are not matched by anything in FOSS. Desktop linux is woefully insecure compared to these platforms. I don't want it to be, but it seems that, unless you are ready to use Qubes, no one has the time and effort to further the security of desktop linux in any meaningful way.