This is complex. I am glad that you queried Van Dorn's desire to co-operate with Johnson. Somehow he does not seem like the sort of person to give up an independent command to serve as a corps comander in someone else's army. Two parallels here are Kirby Smith's reluctance to accept Bragg's direction in Kentucky and Jackson's willingness to join his Army of the Valley to other fiorces in Virginia. I think that we will all agree on who was the greatest soldier.
Did Van Dorn SERIOUSLY try to get to Shiloh?

As to his strategic judgement, I think that the third extract I posted is very relevant, so I repeat it:

Head Qrs Trans Miss Dist

Van Buren, March 19 1862

General,

I march my first Brigade towards Jacksonport, Ark, tomorrow. All the troops here will march in a few days to the same point - I will probably have on White River by the 10th or 12th of April, twenty thousand men or more - and about 70 pieces of Artillery.

It was my intention to attack the forces near New Madrid and Point Pleasant from the North by Greenville - what do you now advise? There is an army of about 20,000 men of the Enemy's, north of this in Arkansas - but they can not be subsisted long - nor do Ithink they can do much harm in the west - We can not subsist here - I think it is more important to save the Mississippi River.

Answer me at once, please. I start for Little Rock the day after tomorrow.

D. Maury AAG.

Three points:
a. At this point Van Dorn is not thinking of close cooperation with anybody, but is open to co-ordinated but independent action. He does NOT use the word "concentration."
b. It did not take a genius to realise that the Mississippi Valley was threatened. Winfield Scott's "Anaconda Plan" had been widely published and commented on - and a Federal push down the Misissippi had already begun. Confederate authorities never valued Arkansas until it was too late. In 1862 it would have been appropriate for Van Dorn to consider that the great and famous river valley would be the post of danger, honour, and fame. It would also be more comfortable campaigning than fighting through the Ozarks while being harassed by pro-Unionist partizans.

On another subject - how seriously did Van Dorn strip Arkansas? Although I admit that I have not been through all his papers the only relevant letter I found was an order to move equipment to Little Rock for safety. Thomas Hindman claimed that Van Dorn took everything - but within a month of taking command Hindman was ordering powder making equipment to be moved from Fort Smith to Little Rock. Doubtless Van Dorn took some things - but he hardly had time to gut the state completely, and Hindman did find munitions equipment to work with.
Arkansas in 1860 was a pre-industrialised region. Even if Van Dorn had taken nothing Hindman would have had inadequate resources. Admittedly Hindman was an administrator of genius - but his talent would have been frustrated had there been no manufacturing resources at all- some were left. It may be that the dog with a bad name - Van Dorn - gets blamed for everything.
For what it is worth my own view is that Van Dorn was a fool - unfortuately he was an ingenious fool.
Tony Brown