I agree with you that most commerical potting soil is much too dense and not fast-draining or aerated enough for pots. Plus, it has components that break down in the pot and make the soil even finer-grained over time.
I also agree that coarse perlite and bark are great for opening up any soil, especially in containers, and double-especially in small containers, or pots that a plant will stay in for more than a few weeks. Perlite is forever, and grit or screened crushed rock lasts forever also.
Pine bark lasts 3-5 years, with coarse bark chunks slower to break down than finer fibers. It breaks down slower than wood shavings!
Medium orchid bark seems too coarse for me, but I tend towards small pots, with only a few half-gallon or gallon pots. Even the one bag I found of "fine orchid bark" was mostly coarser than I wanted. You may be right that "medium" is better for indoor pots, but I mostly pot-up for outdoor pots.
I also don't like orchid bark's price, and the regular shape of it's chunks. The chunks are usually almost spherical, oblong, or football-shaped.
I like screening pine bark myself, so I can get long chips or strands or fibers that (I think) contribute the most lightening and drainage and aeration.
My ideal would be pine bark shreds or long chips 3-10 times as long as they were wide (let's say the general shape of a pencil or popsicle stick, maybe even of a flattened knitting needle). Those get "tangled" with each other, or prop each other up, leaving lots of drainage and air channels ... they tend not to pack tightly together.
Being cheap, I start with pine bark mulch, but I'm not cheap enough to start with crummy Home Depot mulch for $3.50 per 2 cubic feet: full of fines, maybe dirt, wood chips, soggy, anearobic and smelly (fermented on the pallet, not a good thing).
I'll splurge $7-8 for a 2 cubic foot bag of better-quality "medium" mulch from a good nursery, so it isn't soggy and dirty and full of wood chips.
I prefer "medium" over "fine" mulch because the "fine" grade has more bark powder and fine fibers like milled peat moss: I don't want those fines clogging the pores and voids in my potting mix! Probably medium pine bark mulch from a reputable source is already double-screened, but not enough to suit my taste.
Any "mulch" always has some chunks bigger than I want, and a lot of fine stuff smaller than I want, so I screen it a couple of ways.
First I'll use 1/2" hardware cloth or bigger to very quickly pull out things that are too big.
I might put it through 1/2" mesh a few times, and set aside anything retained at all, because 1/2" mesh does let things through that are too long for the pot
A 2-3" twig is too big for a 6" pot, especially if it is thicker than 1/8" and inflexible.
I like long chips and shreds, say up to 1" or even 1.5" long if they are thin and narrow.
I do some hand-picking to remove anything that is too big. I try to reduce the bulk of the mulch in this step, so that the fine-screening goes faster.
Those very big chunks I either use as mulch, or save them to break them up later and re-screen them.
The hard part is to get rid of as much of the fine powder and fine fibers as possible. 1/4" hardware cloth is all I have for that, but I wish I had 1/8" mesh to work with. Even then, some of what passes through 1/8" mesh would be desirable in a mix for very small pots or propagation trays with 50, 72 or 128 cells.
Probably anything over 1/10" is desirable, and SOME finer stuff to maintain wicking, if the other soil mix components don;'t provide enough wicking.
Anyway, now I try to shake my once-screened mulch through 1/4" mesh, discarding anything that will pass through as too small. That "powder" is great for outdoor soil, lightening clay in raised beds. But it clogs up potting soil.
Using 1/4" mesh is tedious, but every bit of fine stuff you can remove gives your roots more air and speeds up drainage.
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Sometimes, to reduce the bulk that I have to fine-screen, I will use a 1/2" mesh at a steep angle, to try to separate most of the big stuff from most of the small stuff very quickly.
(I don't throw away either what passes through or what is held back. But what passes through, I will re-screen later with the 1/4" mesh.)
I set the 1/2" screen at a steep angle, and pour the mulch over it quickly and shake the screen so it runs right off and only a little has a chance to pass through. What DOES pass through most rapidly is mostly fine stuff.
Now I can re-screen that with 1/4" screen, and still remove most of the "powder".
I think this saves time overall, and lets me remove more of the fines in less time. But If I ever find cheap 1/8" mesh, I'm buying a square yard!
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Maybe you could get the mulch really dry, wait for a windy day, and then winnow it so that the fines blow right into an outdoor raised bed where they are needed. I haven't tried that.
