Yes, the polyurethane bushings use a slip fit. That's a polyurethane to steel interface, and they're designed that way. And honestly, I don't even use stock LCA pins with those, I use greaseable LCA pins. The greaseable LCA pins are a single piece, there's no step down for an inner shell to press on. So with a greaseable LCA pin and the older insert-style poly bushing design you totally eliminate the inner shell. You can use stock LCA pins with poly bushings, but then you need to re-use the original inner shell. And either way, the poly bushings should be TIGHT on the LCA pins. Like those Proforged poly bushings that come with inner and outer shells. Try and push the inner sleeve out of those things. You'll need at least a vise, more likely a press. They don't just slip in and out loosely.
A "slip fit" steel-on-steel joint is a terrible idea. The whole idea is that the LCA pins are a press fit into the inner shell, and the rubber is a friction fit on the inner and outer shells. There's no clearance to create slop, all you get for movement in the pin is from the rubber bushing. If the LCA pin slips in and out of the inner shell, you've got slop. Not to mention a steel on steel joint you can't lubricate. Where exactly are you going to drill though the LCA to go through the shell and put a zerk? The outer shell is surrounded by the torsion bar lever and the load bearing parts of the LCA. If the pin can slide around in the steel inner shell, it will hammer that thing oblong in no time at all out on the street.
As for the LCA itself, it's not "trapped". The torsion bars can slide back and forth a good 1/4" inside the sockets. If your LCA slides back a forth a 1/4", you have serious problems. The strut rods (not the torsion bars) are supposed to hold the LCA's in place. Which is why I use adjustable strut rods when I change over to poly LCA bushings. The length of the strut rod is a lot more critical if you use poly LCA bushings. Partly because the LCA can slide a little, but mostly because there's very little give in the poly bushing. So if the strut rod isn't exactly the right length the LCA will bind. But the strut rods still depend on a tight fit between the LCA and the LCA pin to keep that end aligned.
Like everything else, the stock LCA pins have a tolerance. I measured a bunch of them when I switched over to Delrin LCA bushings because the fit is very important with those. And like most things Mopar, of the 4 sets I measured no 2 sets were identical in diameter. Regardless of the style bushing used, the LCA pin has to be a tight fit. If an OE style rubber bushing is used, it has to be a press fit like it was designed to be. If it's not, you need new LCA pins or a different set of bushings. If the poly insert style bushings are used (the kind sold with no shells), they have to be a tight fit to the re-used outer shells AND a tight fit to either the greaseable pin or the re-used stock pin and inner shell. Yes technically it's a slip fit, but it has to be a tight slip fit. If not, just do a search for threads on failed poly bushings. There's more than a few, and most if not all of them had improper clearances. That's the problem with re-using the stock shells with aftermarket bushings, and probably why the proforged poly bushings now come with their own shells.