I have seen many broken bolts and wollowed out holes on thst style of coupler. That was before we started adding shim washers and tightening them down against the coupler real good.
Nyone, when I assembled it and saw the slop it bothered me too. Loose becomes looser. Welding on the vertical bend likely pulled on it thus expanded it further.
Your post is a good one. In hindsight I would bolt it all together tight before welding on that bend.
A 3/4 washer dropped in there (.093?) and was just about right. The bolts squeezed it all tight so there is no movement and can be no wear.