So how does all of that relate to your internal-strength skills? Dantien/hara usage? And so on? The question in the topic is in relation to "What paths lead to internal power?" In relation to Ueshiba and Takeda, would "plays well with other children" have been a known factor in their I.S. development?
I think you would at least need people that you trust in order to:
A) show you these skills
B) be honest enough to tell you wether or not you are progressing or doing the exercises correctly. Otherwise its easy to get self deluded.
C) When you initially start you need someone else pushing on you so that you can feel the difference between proper and improper movement. Perhaps once you have some understanding of this, you can do tons of solo training because you can recognize the feel on your own.
D) If you have a group of somekind, you are more likely to stick with the training and will likely make better progress since you can bounce ideas off one another. Sure if you are hardcore enough you don't need peer pressure.
At the end of the day maybe you don't need friendship (its not going to hurt), but it does help to surround yourself with commited people who are interested in these skills if for any other reason than having a variety of body types and skill levels to play with.