I shoot a 28 bore on driven birds, 24 or 25 gm loads and do not find I am undergunned at all shooting average height birds, that is not more than 35-40 yds. I would not shoot it on super high birds but nor would I use a normal 12 bore with 28 gm load. I join a team of guns for a traditional partridge day with 28 or 410 and maximum 21 gm load and yes we get our 100-120 bag without loads of pricked birds.
I use a John Macnab sideplated 28; it’s light has 29” barrels and does the job so, as others have said used on average range birds the suggestion that you are undergunned is “bobbins”. Just point it in the right direction and pull the trigger at the right time!