Re: aikido vs jiu-jitsu
Yes, two people definitely complicate things and absolutely you need to try and keep distance and control (or create it)....try to put furniture or something else between you and them, deploy another weapon...etc, etc.
Clinching, well, I agree that it is not something you necessarily seek out...but the thing about clinching is, when you have to do it, you simply have to do it. It is about gaining or loosing control of the fight and not so much about that freedom of movement or choice you have in the situation. In some scenarios with multiple opponents it is what you need to do cause that is what you have and controlling that space might be necessary to avoid further bad things happening to you.
If you think about it, clinching is really the same thing as irimi nage, except a little closer than what we typically are used to. You can irimi...then tenkan in the clinch placing your opponent between you and the "multiple".
So, that is the thing for me. It is not about what you'd like to do, but what you have to do.
So, imo, the clinch and working it, is absolutely one of the core things everyone should know. It is one of the core, basic things I teach and work with guys on who are not concerned with learning BJJ, but the basics of fighting. I also work with them on other variations and distances with iriminage.