Explain no more crossbows then, that wasn't magic that was technological progress that inexpilcably went poof, or explain using armor that is less protective than the armor used two hundred years ago. Not everyone in TES uses magic, the nords are extremely opposed to it.
I figured the crossbows were a Dunmer thing. They've never appeared anywhere but in Morrowind. For whatever reason they never migrated into the rest of the empire. This is a bit like how crossbows were used in China centuries before anyone in the west used them.
There are some signs of advancing imperial technology. The Blue Palace is centuries ahead of any other imperial building architecturally. They've never had domes before (White Gold Tower doesn't count, since it's Ayleid). On the other hand, Sentinel had domes... meh. The mills are another example. Those are a lot newer than the design of things like the ships; the sawmills are especially interesting.
What really bothers me is the lack of magitech and any kind of infrastructure aside from some simple roads. Even in Oblivion the Imperials didn't have forts, wheeled transport, signal towers, etc. How the heck did they run a continent-spanning empire? You'd think, given their cosy relationship with the mages guild, they'd have teleport networks for officials, magic lighhouses, etc.
Ultimately, you have to accept that TES just has a technologically nonsense world. The use of technology, both mundane and magical, is basically random in every game. It bugs me sometimes, but not nearly as much as the buildings with architecture that should fall down or the collapsed piles of rubble with no sign of ceiling damage above.