I didn't watch the linked videos, but I did read the comments : a lot of them recommending Jo work.
In my opinion ... for effective (and I mean real effective) use of a SPEAR ... if you ever (EVER!) turn it around and use the wrong end : you're a complete idiot, or just messing about.
Spear is completely and utterly different to a stick. Deal with it.
Wow. I mean, really, wow. You're basing that on what? Do you know what the thing is on the end of a yari haft? It's called an ishizuki. I've seen a huge number of antique ishizuki and they were *clearly* not just decoration. One of these days you might want to get out and look at a few antique ishizuki and I think you might want to revise your opinion. Often made of iron and often with a point as well to reduce the impact area to a very small point, they were well regarded as impact weapons in their own right. Some are downright vicious looking and one could easily fracture a skull.