I think it was both to do the best aikido he could do and the best all-around martial art he could do. And to him, the best martial art would naturally use aiki. While modern yoseikan is a single art (though I thought they had "divisions" for aikido, judo, karate, kenjutsu, etc.), Minoru Mochizuki maintained an "aikido" class until he left Japan at an old age (mid-90s, I think, around the year 2000).
Anyway...I see you're in Perth. Have you trained with Unno Sensei, Mochizuki Sensei's old student?
I am not that clued up on the YWF but I think they do have categories for their techniques such as aiki, kempo, jujitsu and kenjutsu etc in their syllabus.
Unno Sensei told me that the Yoseikan aikido (actual aikido techniques) used to be a lot more combat orientated but had become a lot softer to cater for more students. He also said because the current senior aikido students are also judoka there is a greater emphasis on judo techniques. In Unno Sensei's case his aikido was influenced by karate and Yoshinkan and Tomiki aikido.
My comments before weren't meant to criticize Yoseikan Aikido just stating from my experiences that Yoseikan relies on its judo and karate techniques in order to be effective (more efficient) where as other styles like Yoshinkan and Tomiki seem to have better aikido techniques as they have specialized in that area.
Yes I trained with Unno Sensei for about 14 years.