I agree there is some 'movie' logic at work in Jedi.
Absolutely the Rebels, with the plan they had to destroy the Death Star, did not need their entire fleet, or an entire fleet. A small strike force would have sufficed as ultimately the squad led by Lando is what does in the DS. The shield generator is movie logic too, as placing it on the surface and not within the DS itself exposes a crucial security gap. This could be read as simply Imperial hubris or bureaucratic oversight, but still. So it's absolutely that Lucas wanted (and we wanted) the BIG BATTLE so we got the big battle. If the Rebels had extended their idea behind the capture of the Imperial Shuttle to say the capture of a Star Destroyers and its compliment of fighters, then that's a plan that makes more logical and practical sense. I love Jedi and the battle so I don't have huge problems with it, but it's clear from what behind the scenes stuff we've seen Lucas really, really wanted a planet of Ewoks and a Death Star and everything had to fit in from there. The infiltration of the shield generator was unnecessary when your ultimate aim is to launch an attack with the Rebel fleet, which can destroy the generator from orbit (Han destroys the entire forest anyways
As for my own personal view of the rebels, and that's all it is, I always pictured the Rebels as very scattered and resource poor. What we see in the OT is them consolidating and marshaling their forces and for me, it is the combined rebel fleet at Endor, though I do agree it would make enormous sense for them to leave behind assets for continuity and support.