Padmé lead with JMK in the comp for the CAT tier got 3 stars for a close friend of mine. (I had already beat it with LV on my first try...albeit with only LV and Thrown left standing...so I wasn't going to pay 2200 crystals for some shard shop currency just to try a different squad).
Neither of us 3*'d the Razor Crest one (again, I just threw LV at it not knowing the difficulty and got mostly wasted. 1*/minimal victory, but since I won I couldn't experiment with other comps).
Next month if people haven't already put out videos on how to get it at 3*, I'll play around with comps and retreat rather than win with less than 3* so that I can share more info.
Of course, that would require them not preventing me from trying since I have 7* RC and 7* CAT and I'm not actually supposed to be able to attempt this thing at all...
But in the meantime, yeah. I think it's a little weird that they're putting r3 requirements and 4Mgp requirements on this thing. While it's clearly beatable via brute force (as my LV first attempts showed), there's no way that you brute force it at g12.
My guess is that specific comps make it pretty trivial, but most comps struggle to brute force it without a GL, no matter what your relic levels.
Advice to people struggling:
For Razor Crest, try Jedi Knight Luke (L, modded with 0 speed), with your fastest other jedi in the comp, plus GMY, plus a couple assist callers. Use HeroesArise on the first turn, mass stun the Imps, and then go to work with GMY, calling JKL's Heroes Arise again frequently (every time you can, basically, if JKL is below about 75% TM. Above that you might wanna just take a look at everyone's TM and see if you're better off waiting for Luke to use it on himself and thus reduce CDs faster).
For CAT, try Padmé lead, with JMK, GK, and GAS in the following crew if you can arrange it. Remove Maul using anyone who has a lot of stacks of Courage, then try to hang on.