I shoot geese with a 24" 10 gauge "turkey" gun. I shoot doves with a 20 inch 20 gauge side by side coach gun, I/C-Mod tubes installed. I have shot ducks with that 20 gauge coach gun, but I prefer my 28" 12s, either Mossberg 500 or Winchester 1400 auto.
There's not really any rules that you have to use this or that and if you can adapt to the different handling, hey, why not use a coach gun on doves? It's quick, it's light, it works for me. Don't tell me it can't be done 'cause I do it and do well with it.
It ain't the only gun that can be used on doves. I've killed 'em with a Mossberg and my Winchester, too, and HAVE used my 12 gauge 28" side by side for dove and everything else in the past. I just sorta like the little 20. Now here's something even I think is goofy. My hunting buddy has me loading him some 10 gauge 6 shot for his BPS to use on doves. ROFL! Who am I to tell him is dumb, though? LOL He likes the gun, but that's a little ridiculous. The gun, BTW, has a 24" barrel on it just as his 835 ultimag does. But, the thing is up near 10 lbs. Ain't gonna be the quickest gun to the shoulder, put it that way. LOL
I own shotguns with VERY different handling characteristics, yet, I adapt myself to them. That little 20 is very whippy on high, sustained lead shots, but very quick to change direction on those birds that come in juking and jiving at close range. It will reach out just as far as a 28" gun, though, just requires more swing concentration and follow through.
Never hunted grouse, pheasant. We don't have 'em down here. I'm thinkin' my 20 or maybe my old 12 side by side, if it ain't got too much choke (M/F fixed) would be the tool. My loss, I know. One of these days.......