Should ANY 16" barrel AR be able to hold the last round bolt open when using an H buffer and Wolff buffer spring? Using IMI M193.

Yes, but then again, maybe.

If your gun is cycling reliably (picking up the next round and loading properly) then it should not have any problems.  I make my own 5 oz buffers on my lathe, which is a little heavier than an H2 buffer, and use the Wolff spring on all of my shorty stocks.  I can't say that I've ever had a problem that wasn't ammunition related.

That being said, if you're using underpowered ammunition, you may experience a problem from time to time.  Stick with the load you've listed or any other full powered load and you should be just fine.   You'll notice a firmer recoil stroke with a more authoritative return to battery.

Tom