If you "might need" some else's 7' hose when in a cave you need to seriously question your training.
However in the event I do need to share air with an OW or single tank diver I would much rather use a 7' hose then a 3’. Assuming you could just head to the surface in an open water environment makes me again want to mention you should question your training. That's not always an option.
This all of course assumes I'm in the cavern/cave environment which is the only place I dive my sidemount configuration.
I would say my training is pretty much above par. What ever it is you are blathering about, is another story. But you go ahead and dive and do you.