My opinion about this subject is thar IP has been/is part (in various degrees) of combative skills across eurasia for thousand of years, but is not the Holy Grail for martial awesomeness that some people claims IP to be.
Oh hell ya it is. Oh good Lord it most certainly is!!
This boils down to vantage points again.
Getting hit or kicked by it, or trying to throw someone who gets it, or seeing your naginata, sword or twin sticks completely blasted right through or controlled as if they had little meaning can be quite alarming. And traditional techniques, for the most part, just simply will not function anymore on someone with good IP/aiki. Hence the reason for so many of the legends or greats in our past.
This stuff made and it will continue to make....legends.
What on earth do you think so many teachers are being impressed by? A better way to make a quilt?
What would impress so many of the jaded, been there done that pros I keep meeting? This includes Judo, MMA and Bjj people as well.
Anyway, the only problem is you first have to *get it* to even have or hold much of an opinion *about it* in the first place. Understanding and getting this and then adding a study of (actually *martial*) martial arts is the best edge you can possible have. Period.
Most will tell you that once you start to see the pieces put together -you see it everywhere and you finally understand how it was missed by so many.
It is the foundation for all we do, right there in your face and people missed it, But after training it for a while...it becomes as Ueshiba said:
"Takeda opened my eyes to true budo!"
I can't tell you how many guys with decades in Japan have said the same thing about me or to me regarding this work. I take it all in stride...it isn't mine and there are others teaching it, so how can anyone get an ego about it? It is the truth of budo, but no single person really owns it. We need to see past the individuals and put our hands to the work itself.