I am reluctant to believe broad generalizations about any animals, including us humans. It's popular to generalize on web pages because they're trying to attract as large an audience as possible with the minimum amount of effort. That's why real scientists and care professionals rely more on evidence-based information than on "here-say" passed along from one person to the next with no evidence provided of their claims. As a professional animal researcher, I try to find (or develop) hard evidence of something before I blindly believe or follow it.
When you're talking about how genetic combinations play out in the resultant offspring, it's massively complex and comes down to chance as much as science. That's why there is so much variance within a single clutch just like there is in other species - mammal litters, human families, etc. The fact that a large part of that variance comes from the individual parents vs. their species makes it even more of a "crap-shoot." I suggest choosing a good, reputable breeder and then consulting directly with the breeder, especially about their history of individual breeder birds and pairs. They all keep photos of their breeding activity - breeders and their offspring; it's a big part of their business. Plus they know something about the disposition of those offspring too. Some they can pick up when they're raising them prior to sale; some they hear from the buyers since many buyers like to keep in touch with the breeder to ask questions and to proudly display pics and tell stories about their parrot companions with the people most likely to appreciate them - the breeder(s).
This is the most complete list I know of regarding all of the different macaw hybrids with pics and mix of species for each one. They repeat the same story about the dominant male genes of Harlequins but provide no evidence or links to authoritative sources on the subject. So I'm still suggesting getting down to the individual parents level to find hard evidence of what you're likely to get from any particular breeding pair. It's best to work directly with a reputable breeder anyway, unless you're adopting - the best way to acquire any companion animal! You can't get better "hard evidence" of your potential bird companion than the bird itself - seeing and interacting with it and learning its health and behavioral status and history from a good adoption source.
