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The Fuji f1.4 counterpart are more expensive but better built and better optically.
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Now, if you look at the price of the Nikon Z lenses, the prices are much higher for similar f1.8 lenses...

Btw, Joju the Fuji 18-55 f2.8-4 is not 690 but 498.

I checked at Heiniger and digitec (629.-)

Non of the zooms you compare it to are as good optically or as fast (the APS-C ones) and they are all more expensive.

With FF, you have either the choice of huge and crazy expensive glass or more reasonably priced but not that great (albeit some exceptions).
In ML land, there is almost nothing. The only example we have so far is Sony (huge and expensive), Z and R which have almost no options.

Obviously manufacturers could release slower more compact FF lenses if they wanted to but they're not going to. So what is the alternative? APS-C.

Florent, we can go on like this, but then you should get ready for some solid "no, it's not true!" There's always a certain situation when one lens of an format will be cheaper or more expensive - but the question also is, what will get you for more or less money

Fuji lenses are made of metal - on the outside. Inside rather soft plastic rules, you hear rattle, focus motors always on, OIS as well, even if the switch says "Off". It's a fairytale created by Fuji users and it is simply untrue.

The Fuji 16/1.4 stands no chance at all against the Sigma 24/1.4. Otherwise I'd have noticed. Keep on dreaming about.     Even if it's my favourite lens of the Fuji system.

Wait a minute: At first you said APS-C lenses are cheaper than FF lenses, not matter if DSLR or ML and all of a sudden you (cherry) pick out the S lenses for Nikon Z? These play in a different league than the Fuji stuff. No clutches and all time focus override, no flimsy, too-light-going aperture rings. No need to OIS as it's in the body - if you try to sail that ship, it's too easy to wreck it.

The APS-C zooms from Nikon and Canon have more reach. The 16-55/2.8 ...  well, just read OL's results about a disappointing yet expensive lens. 960.- at digitec, 24-70 lenses (f/4, as it's equiv. , hahaha) sell from 945.-

Fuji lenses are better built than Nikon's G lenses, this is no fairy tale...

Sigma ART lenses are great but huge. That's my point (besides crazy price if one goes with first party lenses): hence APS-C makes much more sense for me.
I threw the Nikon Z lenses in there because they are "only" f1.8 one yet are huge too and costly.

The Fuji 16-55 f2.8 is expensive but much cheaper than the Nikon 24-70 f2.8 or Nikon 17-55 f2.8 (APS-C). In Nikon land there is no equivalent to it and Canon's 24-70 f4 is shorter albeit a little bit cheaper indeed.

Btw, here is the 18-55 at 498 chf (straight from toppreise.ch): https://www.digifuchs.ch/index.php?ref=tp&advised_product=16743