Lol damn dude, you got some passion for this particular debate. Im going to guess you've had a heated debate in the past about this very same thing?
You seem to be right on all accounts. I would put in the ground to produce a thicker trunk, thats my one aim with putting in the ground. One understanding that you mentioned, I would correct for myself, in that I do not put any eggs in the basket of the ground growing tree. I move on with other things, I do buy others, I wouldn't pass up other trees, I dont wait for that tree. Its ready in a few years, and ill remember it. Thats as much faith and care I put in to it. I could make it grow even faster if I wanted to by fertilising, but I'm in no rush + dont want the added expense.
In terms of time, yes that's a constraint we put on ourselves but, you got me.. I want it faster, its true. I'm not too unreasonable! Dont get me wrong, but I do like knowing I am doing something efficiently. Its just the way I am.
To address 2 of your points, on messy roots and branches, this is true. If I wanted to correct that, i could do what people have suggested, dig the tree up every year or 2, organise the roots a bit and put back. To help with primary branches, I am in fact going to, trunk chop it whilst in the ground and keep it there. It has so much energy and vigour from ground growing that I can get a huge head start on next trunk section+primary branches+wound healing.
In my mind, and I might be wrong, as soon as I dig him up, growth is going to slow way down.
To dig the tree up, I want to have trunk chopped him and had some good growth on a new leader and head start on wound healing. Along with this, I will have an explosion of branches already, which I can select and wire (not needed much or at all on Elm but for general). Then I can give the roots a good sorting out, put in a good sized training pot. 2 more years, repot again perhaps (I would think 2 years will be enough to fill the pot with roots, given that it is a strong vigorous tree), will give me a second chance to sort roots again. At this point, should be in a really good shape
THAT'S THE PLAN! Who knows if it will work out like that.