> Disabling perfectly unrelated features (e.g. fast boot), going through Scary Boot Prompts, etc. are NOT acceptable requirements for booting a non-MS OS.

There is Windows fast boot and UEFI fast boot, which are two diffent things. Sometimes vendors support only Windows fast boot, and at least then it is perfectly acceptable to force removal of that option.

Also, for example the purpose of secure boot is to prevent modification and changes on boot options and underlying files, which makes it also to be fine to force disabling, until you set new keys for your new OS.