I believe the Empire genuinely wanted low quality, high quantity troops in part because it’s a more totalitarian approach for them. More stagnation below the top brass so that they’re never threatened by up-and-comers, more uniform approaches to all problems, greater emphasis on the state than on its champions, less chance of successful revolt...
Hell, I think Tarkin was almost as annoyed by how effective the Bad Batch were as he was by their autonomy. He seemed annoyed they won the training exercise without anyone dying, and while sending them against Saw’s people was mostly about testing their loyalty, he also didn’t tell them they were taking on guerrillas, and they would have been in a bad spot if they’d actually opened fire.
Tarkin feels a bit like he might resemble a more military version of the boss from Rollerball, who is clearly incensed at someone being good at their job below him.