No. You can have more than one EFI system partition with separate bootloaders on each drive and set their boot order in the BIOS, just like booting from USB or anything else.
This is also possible with just one drive. The efi boot entries for each OS are stored separately in the efi system partition.
EFI can also live in firmware memory.
You can pull the linux drive, boot from the windows drive, and if one of the firmware updates was for efi, windows will trash the entry for your Linux disk.
This has happened for me many times, I had to use a grub rescue disk to rebuild the efi table.
The boot entries live in firmware yes, efibootmgr can create and remove them. The are pointers to the bootloader. Many systems can boot from the disk itself without the entry, the entry just makes it pretty (“Fedora” instead of NVME1).
I’m not exactly sure what you’re suggesting. Isn’t that more or less what I just said?