3 things to observe about this because I'm a 2012 old hat.
1. Apple uses EFI 1.1 standard. UEFI is based on EFI 2.0 standard. This does not make them compatible (the complete opposite actually), but it does make them able to kind of understand each other. This is why one can break the other so easily. Your broken Macs are not Clover as much as they are UEFI being installed over your Apple EFI, and thus your internal NVRAM, real SMC and so many other parts no longer having 'drivers' to load in UEFI (see second sentence).
2. Some brave soul should attempt a MBR install on a disposable HDD and see if it boots. MBR Windows most certainly works so I don't see why that wouldn't (especially in that it creates a virtual 'EFI Partition' in RAM to load from/to rather than playing with the real NVRAM in your Mac).
3. If doing so, Clover is not actually helping with anything, and most of the help it would attempt would break things, so prior to this, a blank placeholder config.plist should be created. If loading safely but not booting, even auto-filled entries may need removing from Clover boot menu.
Clover used to work for Macs, not sure when that changed but probably El Cap.