Today I planted two more Japanese maples. This time across the yard from the other two mentioned above. These new trees are in full sun and do not have the board beneath them. It is my experiment to track and see if there are different growth rates, how the roots look, sun or shade, etc. Since we are soon heading into autumn here in Michigan a lot of nurseries have their stock on sale. I'd love to purchase more variety of trees to grow for bonsai but this is enough for awhile.
I would let the dissectums grow freely. They are beautiful in the garden, but less suitable for bonsai imho.
Maples are often grafted. Did you check for ugly grafts? This can be difficult to correct.
I have about 10 maples, I think 7 different species/varieties. They are beautiful and one of the prettiest sites in my garden is my big maple at the end of the afternoon, when the sun shines through the leaves. I'm growing them for bonsai, but it is not likely I will use them all. Some of them I'll just keep as beautiful garden trees.