Lord Sovereign
The resident Britbong
Except that, again, the Tarkin Doctrine is explicitly not about military efficacy as a primary concern. It is a doctrine of intimidation, bluntly and explicitly so. It's about sweeping iconography, not punative standards. They're not stringing up proven rebels, they're obliterating whole planets for the crimes of a select few politicians. Mass destruction of the uninvolved.
The Tarkin doctrine all but incites rebellion. The Rebel Alliance is like catching smoke with your bare hands, not something you can hit with a hammer. And by whacking it with that hammer, you just disperse the smoke more and more.
That aside, wanton brutality gives subjugated worlds the impression of "they are going to kill us anyway, so what have we got to lose?" I've never got how the Romans, a pre-industrial civilisation, understood how to keep an empire together better than a galactic level civilisation that has been space faring for over twenty thousand years.