I must say that I grow all my seedlings in potting soil, 24 seeds to a #3 pot. I keep them in pots for two seasons, before planting them out in the fields. My working space makes it convenient for me to do it this way.

I’m not sure that my results show anything different than you have discovered. Other than, much like yourself, I’m not a big fan of perlite. It seems to me that perlite is abrasive, and that tender roots don’t like that, particularly when used as an initial medium to start bagged seeds.

I’m glad to see that you got relatively good results with all of your medums though. For myself, I like the idea of “live” soils, which is one reason why I use potting soil. It would seem that one might get more soil organisms using it ? If one thinks that that might make a difference.

Also I think it’s reasonable to look into the clay grains you mentioned. My sense has always been that seedlings get a certain amount of shock, when transferred from the open medium of their seedling pots, into the much more closed clay soils of the fields. That first year in the fields seems to be a bit of a struggle for them, foliage increase-wise, when compared to their increase rate in the pots, and their subsequent years of growth in the fields.