A lot of that sounds good in theory but the truth is, 3 1/2" 12 gauge shells offer nearly indentical ballistics and pattern to the 10 guage. There is a lot of nostagia with the 10 gauge but sadly, the 3.5" 12 gauge has made it obsolete.
Yes and no. For instance did you know that the ten gauge can be loaded with THREE OUNCES of lead, and still stay 3000 psi below a 12 gauge 3.5 inch shooting 2 3/4 ounces at about the same velocity? Seriously, a 3 ounce slug! (or birdshot if you want, not that lead shot is legal anymore) We can't compare the a 12 gauge 3 oz slug, because you can't safely fit one in the case. The problem is...you'll never see it on the shelf, the demand hasn't been deemed high enough big name factories to market it.
But, I'm a handloader and chronograph, and pattern board type of guy, not a hunter, so I do rely on both theory and graphs, and pressure curves, and I do end up with strange and wonderful loads you aren't going to get off the shelf.
The marketing line is, "the ballistics of the 3.5 are identical", but they always compare apples and oranges to get those numbers.
The load compared that I've seen always a ten gauge 3.5", running light and fluffy steel shot, at 10,500 psi, to a twelve gauge 3.5" running hevi-shot, or alloy shot, at 14,000+ psi. When you do that, the external ballistic numbers are almost identical
There was also a very influential Randy Wakeman article that compared the factory selection of 10 gauge (7 or 8 loads at that time) with 12 gauge (78 or so loads) but most of the selection he compared
wasn't 3.5 inchers in the 12 gauge.
But yes, the factory hasn't been our friend, and seems determined to let the 10 ga languish. If all you ever buy is the loads that you can get at Wal-Mart, you might be better served with a 12 gauge 3 1/2 inch.
It's not nostalgia that fuels me and a bunch of others to keep playing with the ten gauge, it's the possibility for interesting things. The biggest problem with the ten gauge today is SAAMI. SAAMI is a standards organization. When they blew out the ten gauge to 3.5 inches no one bothered asking for a pressure increase. Steel shot is so light, what would be the point? Then they came up with all these cools alloys which were as heavy as lead, and when they blew out the 12 gauge case to 3.5 inches, they knew the needed more oomph, and asked for and were allowed a substantial pressure increase.
This doesn't matter to handloaders, because few of them are so foolish as to use the weakest factory barrel allowed under SAAMI specs, and ......yaddda, yadda, yadda, yadda......
Those who have ears to hear, let them hear....my GF wants me to take her to lunch.