The wobble you describe is the looser tolerances Mossberg uses rather than Remington. This, to some, is " not good quality" however in the field, this can save your a$$. By having a little play, should sand, dirt, mud, etc. get in there it will still function without issue. It should be cleaned as soon as you can, but won't leave you stranded. The "pinned" forend you have can not just easily be swapped out. In order for you to swap the forend you'll need another slide tube assembly, the fore grip of your choice, and the slide tube nut. The newer designed forend has its merits though... Since there is no actual tube moving, there is no scratching. It's a molded plastic housing sliding over the mag tube instead of metal on metal.
I hope this clarifies anything, and if you have any more questions let me know.