Heroic rancor is all about continuously removing turnmeter from the boss so that it (preferably) never takes a turn. If you zeta Vader's lead and let him lead your best Empire and sith characters, you can solo it, yes. Save Tarkin's AoE for occasions where the rancor has a high amount of turnmeter. If you don't have a full team of empire/sith characters you could add characters that remove turnmeter with their basic attacks like QGJ, Rex og Teebo (when stealthed).
Other characters who remove turnmeter (buy not equally well) are https://swgoh.gg/characters/f/remove-turn-meter/