I think that removing standby sharing from clones would be a sufficient "nerf" for GAR, then I'd like to see the other factions brought up to their level. Vehicles need a rework and it sounds like they are addressing that.
My thoughts, in no particular order:
I think droidekas need a point reduction, at least 10 to 20 points.
I'd like to see something like cycle on the HH-12 and remove cumbersome, then it might get more use.
Red defense dice for Han- think Adepticon promo Han 🤣 . But that would bring him up to Rex's level.
Buff Leia to Padme's level, maybe give her Exemplar and/or Authoritative.
Jyn and the Pathfinders could use some help, something to make them more survivable or at least up their damage so they can hit harder before a single squad of stormies blows them off the board.
The Empire has a lot of versatility, but most lists I see revolve around shoretroopers with little variety- maybe making dewbacks and speeder bikes more competitive would shake things up.
Perhaps a points increase to the T-21 to discourage shoretrooper spam.
Points reductions to all upgrade trooper weapons and perhaps extend that to the extra troopers in general. Getting more models on the board will help everyone's offense and give everyone a bit more health. This could encourage more GAR focus on fewer activations but higher damage and health.
Snowspeeder 2.0. Revamp the whole thing, or cut its points cost in half, either way it's worthless right now.
Anyhow this is based on my loc as l meta and experience playing Rebels and Republic.