That's not really how it works. Making it more progressive allows you to run more sag, because it will ramp up more at the end, that's not "mid-stroke-support". If you want it to not blow into the travel more, using just the spring, go more linear, but you might have to run it a lot stiffer and hence, it will be harsher. If you want mid-stroke support, you do it with damping, assuming you have a decent spring curve and because you can't just wildly change the spring rate curve and assume the damping is going to be set to it, it's not. Yes, I've tried more and less spacers.
It can work that way. instead of running more sag, you run the same amount of sag as with the higher volume. So, it absolutely MUST ride higher all through the travel. The fact that you have not increased the compression damping means that it can still plunge into the travel under certain conditions, but it will be at a higher ride height.
I personally, would never go more linear to cure this problem. I've come up through coilovers on every type of racing vehicle (using a linear rate spring) and after all of it, prefer the advantages of a smooth rising rate airspring on every single type. From F1, to Dakar type Rallye cars, Motocross bikes, Indycars...........and mountian bikes.
Running too linear almost always results in too much reliance on damping, causing spikes and using giant foam bottoming cushions, which are a crappy black art all to themselves. From my personal bike experience, too linear always required a higher spring rate, or in the case of a coil over, too much preload. Otherwise it would just sag too much.
The main disadvantage of a rising rate air spring is the high initial force, which obviously, the negative spring addresses to some degree. The other main complaint is seal friction. Interestingly, seal friction increases with an increase in compression damping. As the higher damping resistance causes pressure spikes inside the shock, so it also increases seal pressure and thus drag.
So you may or may not want to do it (mid stroke support, or anything else necessarily) with damping. It's all about combining the variables in the most optimum combination. There is no one "right amount" of anything. You just made two assumptions in your argument, that the spring rate/curve was right in the first place and assuming the damping was right, or as you put it "set". The shock companies are making thase assumptions and more when they make their products.
Mountain bike shock damping, as you pointed out, is one of the most basic forms around. It's way better than it used to be, I remember sliding cans with a hole in a piston for oil to squirt through. And I was trying to market an externally adjustable rebound, compression and air volume shock. In 1993. The bike industry would not have it.
So ya, it's better than it used to be, but that shock damping spec in yours and everybody else's is shock is lucky if it is optimum for one specific type of bump with one specific rider weight with one specific spring rate. At best.
If you like it better your way, I'm fine with that too. I will continually preach that there is no, one right answer. I've seen too much crazy stuff go too fast to be that closed minded.