Just thought I might throw in my opinion on this but I have a saved response from Take Sensei I got from his old website where he responded about his teachers.
Clearly Ishisaka was a huge influence because that was his first teacher in aikido whom he spent lots of direct time learning the basics of the art.
But once he was in Japan and joined with the Hombu Dojo, I believe Isoyama Sensei had the greatest influence on the aikido he became known for. His extremely efficient and powerful style of aikido DEFINITELY comes from Isoyama Sensei.
I have it from a direct student of Isoyama Sensei that Take Sensei spent an enormous amount of time training under Isoyama Sensei back when Take Sensei was taking over and running his dojo in Osaka. Isoyama Sensei would come from Iwama and test many of his students and then train Take Sensei behind the scenes as well.
Clearly you can see the incredible similarities in their respective styles of aikido. The way they do iriminage, the very sharp movements, the deflections.
Just my opinion but I have talked to a guy who has trained under Isoyama Sensei since the 1950's. No doubt Take Sensei learned Caligrophy from Abe Sensei and some of the more mystical stuff as well but his very sharp, martial approach to taijutsu comes from Isoyama Sensei.