The Gold Squadron with TLT, stressbot and title seems to be the best ship in the game right now by a significant margin. Unless one is willing to buy the Rebel Transport and Most Wanted expansions, I don't see a lot of options for making top-tier lists.

Some of the top lists that don't have R3A2 have one of 2 other upgrades that are also only found in Epic ships: R5P9 and C3PO.

Here are two lists I'm aware of that don't contain any of the three above-mentioned upgrades and have been having a lot of success:

Corran and (super) Dash

"Danger Zone" (3 TLT Tactician K Wings including Miranda)

I would guess that substituting a standard Poe for Miranda in Danger Zone would work well if flown properly.

I don't have an E-Wing so I haven't given much thought but I'll be Corran plus Miranda plus a blocker would be good.

What am I missing? A tougher question: how does one approach the problem of making the a top-tier rebel list without using its best ship?

One thing is, if you find something new and supprising. Good example was K-Wing danger zone at Worlds. No one expected 3K-Wing list.

I think a lot list can work, one's better, one's worse.

Started it with Meta lists too. But know working on a way to find new lists, that are effective and less known. As if you put down for example Worlds 2 list or Worlds 1 list, most know it and as it's popular, a lot fly it or variantions. So most know how to handle it.