Well for one, Linkword only teaches visualisations for genders for languages where it's not possible/very difficult to figure out the gender of words from the words alone. Spanish doesn't really have this problem, as you can most of the time figure out the gender from whether the words end in 'o' or 'a'. So the boxer visualisation isn't used in the Linkword Spanish course as it's not needed. The course simply explains the pattern of genders for endings of nouns. Also, not everyone is clued up about the origins of words. Realistically, how many average UK school students would know be able to trace the origins of the word 'horse' back to 'caballo' in the way you described? That's pretty specialised knowledge really. It's far easier and more stimulating to simply use a Linkword style memory hook instead.