The Rebel’s being outnumbered in space is sort of irrelevant as their plan is a quick strike - they don’t really need to out number or destroy the imperial fleet - just deliver one payload at the right time.

The battle hinges on the land battle - so surely it would make more sense if the sail barge showed up to save the day at the shield generator?

I played around with this idea ages ago - a sort of PT solution to the ROTJ problem that might be to your liking.

You’d need to joint edit this with AOTC.

In AOTC - have Jabba one of the separatist warlord. He would be bringing his Droid Legions to the cause.

In ROTJ - Jabba he has since become an underworld kingpin. you could introduce some leftover droids to his palace. He still has control of the droid fleet and legions, which lie dormant somewhere. The Han rescue is now a two-fold mission. Rescue Han, but also gain control of the droid army.

This was originally part of a much larger idea if you are interested - where ROTJ is set much later and the Rebels are now much more powerful.

The crawl would establish that through a daring attack, the now huge rebel movement has gained control of the surprisingly lightly defended imperial capital. They discover the plans for the DEATH STAR II, however because of the relentlessly attacking Imperial fleet, they can do nothing to stop it’s construction.

Leia and Lando go to rescue Han from Jabba, but also to seize the ‘key’ to the droid fleet (I’d assume it would be an extra character that they could abduct during the sail barge sequence who would have appeared in AOTC.)

Endor would now be a droid control station, which is lightly guarded by imperials. Perhaps R2D2 would ultimately control the entire droid armada?

The Emperor would reveal that he allowed the Rebels to capture Coruscant, knowing that ALL their resources and staff would be put in one place, and by destroying the city planet, he could ultimately stop their cause. A hornet’s nest sort of trap.