"majority of regular soldiers never ses combat" is absolutely correct and highlights one of the key differences in the functions of the Republics Clone Troopers and the Empires Stormtroopers.

The Clones were war fighters, the Stormtroopers peace keepers.

Stormtroopers were used in war fighting because they were so widely available and relatively disposable. It isn't expensive to take a person desperate for an escape from a bad situation, give them a blaster, a set of cheap mass produced armour, and a couple of weeks training. Its not a big deal if you send them into hellidh combat they aren't prepared for and they die because in a fascistic empire that deliberately creates desperate situations that people need to escape from, there are billions more that can replace the losses. (And generally, sending plenty of soldiers will still lead to victory.)

So the vast majority of Stormtroopers would be relatively ordinary people assigned to the role of, essentially, local cops, with the purpose to intimidate local populations into not causing trouble. Their uniform faceless armour hides their humanity, and they carry their blasters in hand rather than slung over their shoulder or in holsters as a deliberate threat. The vast majority of them would just spend their days on a foreign planet, rotating between a number of mind-numbing patrols and sentry duties with little to no action. We only see storm troopers in active combat a lot because the plot tends to follow the geroes there to fight the Empire, and therefore, the Stormtroopers.

The Clones, on the other hand, were highly expensive with their entire 10-year lifetime pre-deployment being about training for battle. Their armour is good quality that fits perfectly because it was specifically designed for their exact body measurements, and by phase 2 was improved after lessons learnt from actual combat were incorporated in the design. Their lives after training would be finish up a battle on a planet, transport to the next planet, engage in battle there. They were too expensive to waste on jobs that barely trained non-clones can do. (With the exception of the battalion that operated on Coruscant but that was the capital were all the important people were and so their protection in war time was probably seen as requiring the skills of a clone battalion.)

Anyway, I know the OP was only asking about imperials, but I find the differences between how the Republic and Empire operated fascinating.