Rich,
Heres my "take" on your questions.
There is a big difference in making, drying, firing, potting trees in aclay bonsaipot than there is in molding/making/growing in a plastic training box.
The plastic boxes I/You mention have a bottom of complete mesh with approx. 1/8" holes. I'd say the surface is at least 50% "Hole", this allows for for surface tension breaking and increased water flow and great rooting activity ( which you surely know , since you use them, if they are sitting on the ground
)
MAKING pottery is a different story. I remember when another USA potter started making bonsai pots several years back about the same time I did. The pots were covered with 3/8ish" holes that looked....awful! I doubted their functionality over just a few big ones. Also, the strength of such a group ( I'm talking about 20 in a 10" pot) . I bought a few pots. Sure enough I just bumped one against something and it cracked into 3 pieces.
I have always used 4 or 5 holes in med sized rect., and up to 7 in larger pots. That is MORE THAN ENOUGH. If spread throughout the bottom they afford fine drainage especially if bigger. Water surface tension is more easily broken with a few bigger holes than with a whole bunch of tiny holes.
Now, theres this big "push" for newbies viewing pots to want to see a ton of wiring holes. Well, you don't need them! If you have 5-7 large drain holes in a pot and can't get a tree wired into it....give up bonsai!
I've heard the complaint"If I use drain holes to wire through it tears my screen". Well, my answer to that is to stop using that cheap a#@ plastic mesh, wallboard tape and knitting backing with the tiny holes and use galvanized hardware cloth. You can buy 1/8" and 1/4" Hdrwr. cloth at any good hardware store . It last a long time.
Now, MAKING pots with too many holes is just asking to have a bunch of pots thrown out from cracked bottoms. As pots dry and are fired there are quite a bit of stresses on them and mostpots that crack during any process USUALLY crack from the drain holes. Having a mesh of them in the bottom that you don't need is just asking for it.
But, some folks buy pots for the holes! Especially if "name hype" is involved. But when its all said and done, 2 to 4 larger holes in any pot is enough.
I'm SURE there will be disagreement, but...Thats my story, and I'm stickin' to it!
Regards,
Dale