Sorry, but that sounds utter nonsense Mike - the AVR was essentially a 'rip-off' of the PIC, which is perfectly happy using a single current limiting resistor and the internal protection diodes (with
MANY official application notes showing their use in that way).
You even showed an AVR diagram displaying similar protection diodes, why would you think they are fitted if they aren't of any use?.
But in any case, the two resistor attenuator suggestion I made would easily meet the supposed 'requirements', and at considerably less cost than one resistor and two Schottky diodes