But that rifle was made from a real world SMG, so it doesn't look futuristic at all
Everything in all movies is made from modern components. It's not like you can go buy a real droid from an actual Jawa. But the end result looks far more like modern, contemporary and plausibly futuristic than the silly ray gun rifle Kirk had. Lucas calls them "ray guns". He uses the lingo of his childhood sci fi, but they don't look as retrofuturistic as what the Discoverse people have done.
				
 ENT actually did, precisely for the reason you indicated. This silliness, like Kelvins, is not a reasonable extrapolation of it. It's a higher production budget version of retrofuturistic classic sci fi.