Of course, there is some numerical evidence available from my old favourites, Goodreads and LibraryThing. I had to stay up late this evening, and plugged a list of leading Hispanic sf writers into both systems. I populated my list from Wikipedia and from those listed on web pages which appeared reasonably high up the Google rankings for "Hispanic science fiction writers". I ended up with 27 writers on my list, but took three of them off (Giannina Braschi, Junot Diaz and Sandra Cisneros) because it wasn't clear to me that they are writing sff, and I could not tell which book or books should qualify for my analysis. I couldn't find any books to measure for the other four, Tom Greene, Richie Narvaez, Alejandra Sanchez and Alberto Yañez; I guess that they have been publishing short fiction (or that I simply missed the listings for their books).
It may well be that of the remaining twenty, some are not really sf writers or indeed some may not identify as Hispanic; my apologies to any who think that they do not belong on this list. (Silvia Moreno-García may well be a case in point; she describes herself as "Mexican by birth, Canadian by inclination".) It is certain that I have omitted writers who definitely are Hispanic science fiction writers with solid books to their credit; again, my apologies.
Anyway, here are the results, ranked (as is my usual habit) by the geometrical average of the number of owners of the top book by that author on both systems. In most cases the same book was top on both systems for each author. In a few cases lower down the table, different books topped the author's list on Goodreads and LibraryThing, so I took the one with the highest geometrical average of the number of owners.
In one case, an author's top book on Goodreads scores decently enough in the bottom quarter of the Goodreads table; but not a single LibraryThing user appears to have acquired any of his books. So he is listed at the very end.
There is a very big jump between the top seven (all over 4600 on Goodreads and over 190 on LibraryThing) and the lower thirteen (all below 2200 on Goodreads and under 130 on LibraryThing). I think it would be fair for any of the twenty listed below to describe themselves as "a" leading Hispanic voice in science fiction; Carmen María Machado, Daniel José Older, Ana Castillo, Malka Older, Manuel Gonzales, Silvia Moreno-Garcia and William Alexander would be on particularly solid ground if they made such a claim.
I confess that I have not read any of these as far as I can remember (though I have read short fiction by several); will try and fix that in the course of this year.
Edited to add: And almost immediately, someone has pointed out that I missed Ann Aguirre, whose Enclave has a massive 161,503 owners on Goodreads and 1,336 on LibraryThing; and also Ty Franck, half of James S.A. Corey, whose Leviathan Wakes has an even more massive 190,177 owners on Goodreads and 2,531 on LibraryThing. They certainly belong at the top of the list.
Edited again to add: Ann Aguirre apparently doesn't count, but Bronze Gods co-authored with her husband Andres, has 9,768 owners on Goodreads and 225 on LibraryThing, which would put him firmly in the upper third of the table.
Edited once more to add: For some reason I had missed Michael J. Martinez, whose The Daedalus Incident has 3,654 owners on Goodreads and 135 on LibraryThing. That puts him towards the lower end of the top half of the table.
Edited yet again to add: A. Lee Martinez writes both sf and humorous fantasy. His Gil's All Fright Diner has a very respectable 17,277 owners on Goodreads and a massive 1,095 on LibraryThing.