Here I am -- sorry.
My take on all of this:
What's going on is that the evidence is problematic, and the inherited stories are problematic. So we end up deciding on what version makes most sense.
By the way, just to get if off my chest -- there is no Tittensor MacKenneth. Tittensor is not a French name, it is not a Scottish name, it is an English name, and it shows up later. It makes no sense. So the fact that her dates don't work sorta doesn't matter cause she wasn't there.
Ok. On to other people, and whether or not they existed and what their connections are:
Medlands is following Paul A. Fox, who is currently the editor of "The Coat of Arms," which is the Journal of the Heraldry Society, UK. He was a doctor first, but has been working in heraldry and genealogy for many years, and has a bunch of high level recognitions. Fair enough.
The question, of course, is whether his work in this instance is trustworthy. The reason that Medlands chooses him over Round is that the primary evidence seems to fit Fox's construction better.
J.H. Round's work, "The Origin of the Stewarts," has been highly influential, and is available online. And though Round's work is dated, he was honorary historian to the Crown. So he is one of the Big Guns.
I myself would go with Medlands on this one, based on this: "Round, in his early 20th century study on the origins of the Stewarts, splits "Alan son of Flaald" into two persons, the second being the supposed nephew of the first[818]. However, Round cites no primary source which confirms that this is correct, and it is more reasonable to suppose, as proposed by Fox, that all the primary source records for this name in the latter part of the 11th and the early 12th centuries refer to the same person[819]."
It's Occam's Razor.