You’re probably over-thinking the implications of some of their tech. Bear in mind this is a fantasy game, so while we thought out some of this, there’s a bit of handwavium as well (we weren’t trying to make a 100% realistic alternate history, though we tried addressing some of the big points).
Some of it’s intentional—but for example I didn’t actually know the magazine-fed bullet story, so that’s clearly not implied there, though there’s other reasons for those rounds. ^_~ Some of what you’re assuming is not for reasons you expect (the Legion may have no ideas about Germ Theory, but if a healing god shows up, and they fall into her ranks, and she tells them to use “this stuff” they make a note in the Annals and stock their kits once it’s proven to work). They may not know why always, but they’ve been trained to try and overcome impossible problems, and use their merc funds not to grow exponentially—but equip themselves to solve problems others cannot. For example they can’t make Crimson Seeker rounds, but they bought what they could, and have a couple left from the Godswar.
There’s a few key things in play. One is that the Old Empire had more advanced tech than is currently available (you can see a piece of their comms network in one of the special missions). It went belly-up when the Empire did (what’s up Zora!) but the Legion keeps the Annals which has notes, and it saves certain things in its stores (like strange bullets and relics) and watches for some of that tech to resurface and get re-developed.
The WHY on some of this is not always paralel to our world (remember that some fundamental rules—like alchemy actually works—are not 100% the same, so consequently what develops and when is not either). For example, the reason for jacketing here has to do with containing specific alchemical type bullets (you’ve seen black and red shot, but there are at least two others).
We did do some research on military unit organzations, and the Legion acts like a set of special forces units (small squads who train together, with specialists attached based on missions as necessary). And yeah, they’re a bit more advanced than the folks around them. A chunk of that is definitely tied to being under the personal banner of previous Emperors/Empresses. I agree that they’re pretty neat I’m glad you like em.
PS. On flares—that can be a use. The flares are a bit more complex than appear at first glance because they’re alchemical. So, they can be set to do a variety of colors for signaling. Talk to your group, figure out how your version of the legion uses them You can see some ideas in one of the eps I run on Actual Play (we had an ep where legion flares actually played a big part).