Better glas? No. They have more, yes. But quality wise fuji is damn hard to beat. I had a variety of Nikons, from a D40 up to a D4 and basically everything in between. And I don't know how many lenses I shot, a few hundred probably. The Fujis are optically on par or better. The Kit zooms are actually usable and the primes are just beautiful.
I agree with you on the fact that you have more options when it comes to the used market. No question. But because of the mirror and because all the used lenses are full frame (because film) you will end up with a pretty bulky camera. And as a result of that the camera might stay at home most of the time.
btw: a D series 70-200 would not work on a D3X00 or even D5X00 body because those bodies do not have an AF-motor.
also btw: Fuji has a 50-140mm f/2.8 which is the equivalent to the 70-200s.
And one more thing: You can't use adapters to mount stuff to Nikon DSLRs. The distance from sensor to the mount won't allow for that. So if you would like to take a look at a M-mount lens for example you are SOL.
Personally I think unless you are shooting events like concerts or sports for a living and therefor need the absolute best AF or low light performance, there is no reason to buy DSLRs anymore. I am using Fujis for stills and Panasonics for video myself and those work extremely well.
I got a idea for a t-shirt make a spot like a pocket or something to hold a cell phone
Using an adapter on mirror less with an F mount or other DSLR lens makes it just as bulky as a DSLR. Maybe not to an exact T but certainly close in the same weight. Also just because you don't AF on a lenses doesnt mean you cant use it. I person have a D series that I used to use on a D3300. I recommended this path because again of the options. I am not saying that fuji glass is awful but in the long run if you start on any type of camera the best way to go for an upgrade path is F or EF mount DSLRs. Yes the mirror less fuji is 'lighter' than a DSLR like the 3300 but seriously a D3300 and a small prime like a 35mm is so compact it fits in a purse or even on a belt strap. they are really light and not bulky at all. Im not saying carry around a D4 or anything, but there has never been a time where I was carrying my D3300 or my D7100 and thought 'Oh man I wish I had brought my a6000 cause this Dxxx is so heavy.' and between a 300 dollar x-e1 and a 18-55mm you could buy a sub 200 dollar D3300 a prime 35mm and a prime 50mm. its just a more cost effective system in the long run. It has some disadvantages but for the price there isnt much out there that will get you that quality.
OK, I see we have very different approaches on this topic. So we better end this here.