And you can very easily say that devils are just creatures in whos nature it is to keep their word, and that they lack empathy. Simple.
Yeah, no. There is Blood War - an actual clash of (evil) Law and (evil) Chaos - the whole cosmology
You can certainly do away with alignment itself, many DMs using 5e actually already did just that (and I completely agree with it), but not the actual cosmology and the objective nature of g/e/l/c. Devils are evil manifestations of Law, always will be.