Hi Hans
Thank you for bringing this article to WikiTree and I should say at the outset, that I don't read Spanish, apart from a few words or phrases, and I could have easily missed something in my comments below. Hopefully someone who does read Spanish will correct any errors.
Firstly, no offence to the author or the journal it's published in, but I have some doubts, looking at the general pages, and rules for submission, that the article has actually been reviewed before publication. Certainly it's not obvious that this is a peer-reviewed journal.
Secondly there is another article on the Mendez de Sotomayor family
Cabrera Sánchez, Margarita. "El Señorío de El Carpio en el Siglo XV" (PDF). helvia.uco.es (in Spanish). Aragón en la Edad Media 14-15 (1), 227-242 (1999). Universidad de Zaragoza, Departamento de Historia Medieval, Ciencias y Técnicas Historiográficas y Estudios Árabes e Islámicos
The genealogical table in this article (on page 230 - image 4 of 15) has a dotted line connecting Garci Mendez de Sotomayor (Fernando Llorca Castro's generation IX) to his parents, which I presume indicates that the relationship is unsure, or he is considered illegitimate? Certainly Garci appears to have been overlooked and it is his elder half-sister Beatriz who becomes Senora de El Carpio, and her son who is created the first Marques de El Carpio, and I'm not sure why that would happen if Garci was a legitimate son?
So I think that is probably the point at which someone with better Spanish skills than myself, needs to look at Llorca Castro's article and decide if he presents a valid, reliably sourced argument for that connection.
Certainly up to that generation 10 there seems to be enough evidence to create those generations if they aren't already on WikiTree, it's just a matter of someone finding the time to create the profiles.