Frankly wouldn't be surprised if all armors and weapons were governed by one skill/perk tree in TES 6

Then again, the perk trees for light and heavy armor and one and two handed weapons are practically the same in Skyrim already.
I doubt that would happen though I still wish they would have gone with Sword, Axe, Blunt rather than 1-hand & 2-hand but you have to think from a dev team perspective ... They wanted to make the game more accessible to the masses ergo make the game even more simplified than Oblivion. That's why they chose the way they did it. I just hope in the next game they keep things similar to Skyrim but more diversified like Oblivion and more importantly Morrowind. Now that they have the steam back after how successful Skyrim has been I just hope to god they don't simplify it even further. Otherwise Bethesda just lost a very loyal customer that has bought 2 of most of their games & add-ons/expansions.
And since we have never encountered either of the two groups in the DLC before, maybe crossbows are just something one of them invented. No one complained about curved swords, or the swords the Blades use being different, why complain if the Dawnguard or some other group or race we have yet to see have their own unique weapons.
Crossbows WERE NOT invented by the either faction they were in a previous TES game and all Dwemer Spheres have crossbows.
Like I said earlier in this thread ... The reason crossbows were reintroduced is because they are the weapon of choice of many vampire hunters of lore. (i.e. Van Hellsing)
Spears were also in Morrowind as well as a few other neglected item/weapon types. This is the reason so many people are frustrated.