If locking the bootloader and comparing signatures against keys burned into a secure enclave allow Apple to make certain security guarantees that helps them sell products, I'm all for their freedom to do so.
Why doesn't OP merely champion competition, instead of encouraging regulation of what software others can write, what hardware others can ship?
I too am afraid of general purpose computing going by the wayside, and I have the Precursor phone and Raptor Talos PowerPC machines on my wishlist, just as soon as I wrap my head around secure boot chains in general before having to implement one myself. But niche hardware is expensive to produce, so we're likely left with what AMD, Intel and Apple provides us.
I guess one quirk that IMO is fair to criticize is that it's not necessarily consumers who are demanding to be locked out of their administrator privileges (the average computer user is of course not aware of the distinction of signed vs unsigned binaries), so I don't know where the pressure for secure enclaves really comes from. Is it the data centers buying thousands of chips that don't want to be pwned? government customers who refuse to buy a single die if they can't verify the bootloader? Or just patriotic engineers sensitive to a cybersecurity regime that demands we keep our guard up against enemies, foreign and domestic?