Re: What is "combat"?
Senshusei is specifically an accredited Yoshinkan Instructor course. They don't teach people anything except how much guts they have, and very hard Aikido technique.
Hombu makes it grueling because they want the certificate to really mean something. It's very long because they want to make sure you don't make it unless you're truly in posession of the techniques.
It turns out guys like Robert Mustard Sensei. I think he could perform shomen irimi nage on someone trying to hit him with a car.