Streamlining (something about firearms? I have no clue what you are talking about) doesn't make any sense, and balancing restricts their usage to narrow avenues of RP, which is no fun for players with imagination.
Firearms do add a different type of RP, but it is a lone tasty sprinkle atop a cake emitting dangerous amounts of beta particles.
Is plate your reason for firearms not instantly replacing other missile weapons? Check your so called scholarly articles next time, you glutton, and you'll find better ones. The effectiveness of plate depends on a variety of factors, including the force imparted by the firearm, weight of bullet, and qualities of the receiving steel.
The complexity of firearms, referring to arquebuses, which I assume is the type of firearm being proposed, is, indeed, too much for the casual roleplayer to run with. A huge amount of players barely emote normal bows right, so what will make the multiple delicate steps required of a firearm any more accessible?
What is this new kind of RP? Threatening people with firearms, hitting people with firearms, and shooting people with firearms? A precious few people ever RP taking care of their equipment, so we can count that one out.
Where will this scientific development end, I ask? Personally, I prefer mages and alchemists coming up with interesting developments rather than self-titled engineers pasting something from Wikipedia and calling it innovation.
Except dragon beings and magic from Aenguls do not have the potential of becoming ubiquitously used due to their RP composition alone!
Oh, yeah? For you, perhaps. Creativity will set you free, should you have the mind for it. :)
They aren't as rare as you seem to imply, but they were relevant past the spread and development of cannons, yes. Fortifications underwent changes to adapt to such a weapon, and were still built in a style relevant as time went on, contrary to Tarian's statement.
You're right on the numbers there. Do keep in mind that with the introduction of cannons, the siege question changed from IF the enemies would surrender, to WHEN the enemies would surrender. That's just a nice adage paraphrased; I like it a lot.