Wasnt MaxTransfer workaround for buggy harddisks that could not transfer more than 64K at once?
You should be able to set MaxTransfer to ffffffff on ATA hard drives, there is a fixed upper limit of 1fffe which is impossible to exceed that should be hard coded in the device and you are then supposed to ask the drive how many words to transfer after issuing a command. commodore don't seem to know about the 1fffe limit & they assume it will transfer what they request.
The highest most ATA drives can transfer is 1fe00 because it always transfers multiples of 200 and 20000 would overflow the count. There is nothing to stop a drive from normally being able to transfer 1f800 bytes from only being able to transfer 800 one time because of temporary buffer constraints or sector remapping. If the drive doesn't transfer as much as you need it to then afterwards you're supposed to issue more commands.
There might be hard disks that react differently to how commodore expect them to, but the hard disks are operating within specification. commodore either never read it, or decided it was too hard to implement properly (maybe because it was written in assembler?).
Any problems with SCSI drives are likely to be caused by similar bugs in the relevant .device code. It sounds better if you have can convince everyone that it's the superiority of the Amiga that it requires kludges to work around bugs in cheap hard disks that were made by lesser people for the inferior PC.