Ok, I have never been real clear on threaded vs threadless, I have both types, and personally I can't tell the difference how the bike handles etc; what I do know, at least from my experience, is that the treaded system is actually easier to adjust and work on, I can make small adjustments to the height of a quill stem where I can't do that with a threadless without trying to find a spacer the right size. I get really messed up when I have to dink with my threadless system, plus the threadless system doesn't look as nice. Not only that but with a threaded system I can remove the stem and not bother with removing the headset. I think the only reason threadless came out was because of aluminum and carbon fiber frames, a bike company couldn't make the headtube light enough in the case of aluminum because the headtube would have to be thicker to prevent the quill's wedge from damaging the headtube as you tighten it down to secure it; and in the case of carbon fiber you would have to use a thick steel or aluminum insert to prevent damaging the CF again defeating the purpose of trying to get the bike frame lighter. I guess if you're into cutting your own fork the threadless system is a lot easier in that regard to prepare a fork for a frame. Then if you over tighten a threadless you can damage the headset and or the head tube. Some of these threadless designs are proprietary systems that only the bike manufactures headsets will work.

Here is an example of someone that had an issue with a threadless design that ruined his frame: https://forums.roadbikereview.com/bi...set-18745.html And I've heard of this issue on more than just one occasion. There was some issues similar to this with wedge system on quill stems when steel manufactures came out with too thin of headtube walls and a person over tightened the quill making the wedge bulge out the headtube, but I have a feeling that was extremely rare, not sure how rare the damage of a threadless design as I mentioned above is.