The slide on my Kadet conversion isn't fixed to the barrel assembly at all.
It rides on the inside rails of the gun and moves back and forth as the gun fires.
The barrel assembly is held in place via the slide stop.
Here's one pictured with the slide all the way back.
Bad choice of words on my part in my response, above... (I called the barrel assembly the slide, and mentioned a separate part
that moved... that's what YOU called the slide.)
The barrel assembly is held in place by the slide stop AND
the front of the gun's frame rails. That pretty secure. The rigidity is further enhanced by the slide assembly. In effect, the whole assembly is held in position by both the slide and the frame. The slide stop prevents both vertical and, coincidentally, lateral movement
. It's an interesting design.
Tightly fitting the barrel doesn't really do that much. No reason not to do that, but a LOOSELY fit barrel won't perform much differently than a tightly fit one, because when everything is in place and the "slide" is closed (as before a shot) there's simply not much possibility of movement. The slide stop, I think, is the key: it doesn't allow the rear of the barrel to move much vertically or from side to side.
If the lug through which the slide stop slides is sloppy or worn, you could see some movement and that would degrade accuracy. But if it's snug, the barrel just can't move that much (if at all.)