Realistically, I agree with all you say.

Previously, Lee had drawn [or attempted to draw] proportionate reinforcements away from areas where the enemy had reduced their strength. I believe it was his way of blending sound military logic to concentrate force, while still pandering to Davis and his insistence on defending every foot of the Confederacy at once.

In this case, it appears from this distance to be a reflexive action by Lee in accordance with his military views, and to play any and all of the dwindling cards he had remaining.

The Union river fleet, and the disinclination of many of the western Confederate troops to cross, would have probably been enough to defeat the notion----at this late stage. And, as I said, even if some were miraculously able to cross, it surely would have been too little too late.

Whilst still a long shot, the failed effort to cross in the summer of 1864, was not attempted with a coordinated [both sides of the river] nor, apparently, with an inspired effort.

As an option to the Trans Mississippi troops idling away the rest of the war, and Forrest being tied down by orders to defend territory--it would have been interesting to see Forrest and Taylor working together to make things happen.

As it was, I believe Taylor's primary goal at that time was to get away from Kirby Smith; and Forrest was being distracted from Sherman's supply lines.

Two of the more capable Confederate leaders, and significant infantry forces were being diverted from their very real capacity to "make a difference."

But, even had they been successful, their newly combined force would have probably been dispersed to protect Mobile and other positions, rather than being thrown en masse against Sherman's rear.

Intriguing.