That's not true for a number of reasons. Aikido, as a system was not built for the MMA ring. It doesn't work properly, I know from personal experience. Aikido is not a method to develop power, it's a system. "IP" doesn't sound like a martial arts system to me, it sounds like a way to develop power. It also seems like the "IP" crowd is saying that with this unique method of developing power, you should be able to use this power for all kinds of physical activity. Specifically, you should be able to use this power martially.
This depends. Some systems are still built up around it, where this sort of training is what your work on, but you still learn how to kick and punch. Other people have distilled the IS exercises and just work on that on their own . Other places expect that you already know how to kick/punch etc, and then give you this material to work on (sounds a bit more like aikido where a lot of people had other experience before joining Ueshiba's dojo).
I think some of what is needed to develop this sort of power is still in aikido, if done with IS. Though you would have to organize the class so that more time is spend on solo work (or doing suburi or spear/jo thrusts), then some portion of the class is spent on partner work, at least initially or for newer students.