I've heard this kind of thing before, but my assumption has always been that the people who are saying that don't know how to make a macro that simulates the "buffering" that pressing normal buttons has. But perhaps I'm mistaken; I just never see others writing macros that contain the "buffering" that mine do. Is there by chance a source for this claim? I'm guessing if this is the case that someone did some tests, and hopefully they recorded their methodology as part of that? I'd love to review something like that.
And if it doesn't exist, no pressure. I should actually probably just do my own tests anyway. I have a feeling I know what I'll find, but maybe I'll get proof that I'm wrong!
All of that said, all macro use is a compromise. You're losing something (for example, a certain amount of buffering) in order to get something else (like accessibility). And whether the juice is worth the squeeze is going to be relative to each player's needs. If you're a player like me who can only use certain button combinations without discomfort, there's no way to reasonably play most classes without macros. And that's a time when we should be encouraging macro use, because not everyone has the same needs, not everyone has the same ability. At some point for some players, being able to play comfortably is going to be worth the theoretical loss of some DPS. Especially if they wouldn't have been doing that theoretical DPS anyway because without the macros they would perform worse.
All of that said, I do agree that if there are downsides to macros, it's important to note those downsides so that players who are interested in them can make an informed decision on whether such macros are worth it to them.
If I remember, I'll do some tests tonight and report back the results!