Ok tx bro,
So for a start, android is linux and so is ChromeOS. Both incredibly highly secure linux distributions, with sandboxing and locked bootloaders.
That alone shits on all your possible arguments.
Now to be a little more in good faith, you also have less known variants - that run in RAM like TC, amnesic like TAILS or atomics like fedora silver blue… the list goes on and on. Each with their own protections and security that can go above and beyond whatever you have in mind as an alternative.
Sure, maybe your average pedestrian linux distro like ubuntu is not the most secure option. But it is still one of the most private.
And if you want a linux that is more secure, it is pretty simple to find yourself a secure distro that mitigates whatever brain worm problems with grub or otherwise that has you fixated on.
Security on linux is a skill issue. It can be as secure as you want it to be. It could literally be designed to self-destruct if you want to go full psycho with it.
Now if you are upset that it’s not all magically being done for you in the timely manner you want, then you’ll just have to accept whatever slop is given to you.
But then you don’t really have a leg to stand on as far as complaining about it.