Hang on a minute! Don't go suggesting that now after I cut up a perfectly good link!
The problem with design is that it's easy to get tunnel vision, particularly when you want to use parts that are just laying around collecting dust.
Your suggestion is a good one and definitely worth thinking about. Yep, the chain is a really good idea and I can't think of any real downside to it. It would be much easier to hook up too since aligning holes at either end wouldn't be an issue, and as you say, you could raise and lower the hitch to get the trailer onto the ball without messing with the jack. Well crap! Good job I haven't wasted any paint yet! I guess I might be upgrading the connecting link and replacing it with chain unless I can delude myself into thinking that the link offers an advantage.
Now my Frankenstein effort is looking extremely cumbersome. With a chain you wouldn't even need the sleeve on the draw bar, just a shackle at the end of the draw bar to run the chain through. Sigh .....