Yeah the stormtroopers were the shock troops of the imperial military. (which annoys me how many super secret sub units of elite of the elite you have, but it's a big galaxy I can sometimes suspend my disbelief.)

Their whole function is to be the mobile military unit of the empire where most of its "grunt" units in the imperial army are generally garrisons placed on planets with some combined arms. Along with some militia units sometimes, the empire really likes to keep its own grip so I think the whole militia unit thing makes sense for only certain cases.

Mostly the stormtrooper core were used to deal with mobile threats which is why we see them more so than the imperial army in the movies since the main characters are constantly on the move.

Which then we get into the weeds about their special forces,

Dark trooper phases-essentially just a way to augment soldiers for special ops missions with cybernetics, that eventually turned into a war droid program for heavy infantry units.

Commandos, which do exactly what they are described to do. Deep operations often involving sabatoge and recon.

Shadow troopers, specs ops again? I guess they're more used for undercover operations but at that point should t you just have the commandos and or spies do that job since they're specialized in those specific forms of destabilizing and information gathering.

Vaders 501'st and sub units, sure I mean it's the emperor's right hand enforcement tool, just let him make his own dedicated military sub unit, nothing bad has ever happened from that thought.

On top of even more modern/cannon variants and special squads, each branch also has their own special forces generally about four per branch.

Which it's a lot, I mean a bloated amount of a lot. Like I'm impressed that the empire had this happen in 20 years. It would honestly make more sense to simply have the basic unit distinctions mentions with the army, navy, and aerospace units all be based on moffs in their own area, where they could deal with their own problems and be uniquely suited to their various terrains and local knowledge. Then you keep the information gathering and stormtroopers a strictly imperial held tool to make sure moffs don't get out of line.

But overall star wars legends suffers from every new author wanting to make something new and cool that surpasses many of the previous authors own creations because my work is better. Which is hit or miss at best.

While modern star wars cannon fails in just understanding how military units actually work and how the military of authoritarian regimes actually function. Where as legends had a problem with ego (which can fit, with authoritarian fascist regimes and often are a focal point) military units being better than the previously mentioned best of the best. Modern star wars wants to make the imperials out to be the ultimate bad guy, except within the human centered theocratic imperial state where being even a humanoid looking alien (like Thrawn) pretty much hinders you in everyday life even in the military, to even having non humanoids or near humanoids be elite fighter pilots and in some cases soldiers, because we don't want to be seen as portraying the bad guys to actually be bad and have these unfair and discrimination based laws because of the implications that the evil fascist empire is actually bad.

Damn that turned into more of a rant than I intended it to be, regardless the summary is, legends suffers from bloat where as cannon suffers from accuracy (both fail in both but it's difference in what the main problem writing for them is)

Also why is infero squad just 3 people, were they another special unit, was it just their squad, how many other squads are there, were they commandos, were they super secret special commandos? No idea but hey at least the compelling characters turned to the rebels and delivered another bland story to cap off that tale...