a 21 doesn't have a weight issue, they (most of'em) have a missing trigger issue.
I always get a laugh out of folks who insist that DTs are an advantage on a grouse gun! I can see an occasional advantage to 'tight choke first' on incoming waterfowl, and on far-flushing pheasants. And indeed I almost always use my DT Coggie for ringnecks.
But in the grouse coverts where most shots are taken within 30 yards, and heavy cover makes long first shot opportunities few and far between, my non-selective ST Bernie does it all. Unless you resort to potting birds in trees, I can't think of a situation that calls for a tighter choke on the first shot.
So here's my question for you DT fans: under what circumstances (and how often) would a 'tight choke first' be advantageous for grouse hunting?