I am sure that an AFV that was sighted in the open in WW2 could be destroyed quite quickly, but I am not sure how much operational research went into Whitaker's report of an eight-second life expectancy.
Regarding Jock Columns, I think some things need to be established without taking away from their applicability to the modern battlefield. The initial campaign in the Western Desert against the Italian in 1940 and early 1941 was not really ad-hoc, although of course adaptations were made by commanders based on the threat, demanding environment and extended lines of communications. The force that became 13 Corps under O'Connor had an Armoured Division and an Infantry Division (initially 4th Indian Division and then 6th Australian). They had Corps artillery with something like five regiments of guns plus the artillery regiments in the divisions. They also had, of particular note, 7th Royal Tank Regiment (7 RTR) with Matilda tanks.
The initial Italian invasion force was unmotorized, and after seizing an area of Egypt they settled down in to a series of strongpoints along the coastal road that lacked mutual support. The numerous Italian formations were poorly equipped with armour and lacked mobility. So they were isolated. Jock Columns from 7th Armd were indeed used as O'Connor assembled his forces and made his plan to keep the Italians blind, and they were subsequently used as guard forces. But much of the real work of destroying the strongpoints and setting the Italian army on the retreat was done by tank and infantry attacks supported by Corps and Divisional artillery.
O'Connor carefully planned the offensive after a deliberate estimate of the enemy's capabilities, the difficulties of supply and the nature of his own forces. He knew that the Italians didn't really have answer to the Matilda, so the destruction of Italian strongpoints would be done by Matildas breaking into these positions following Corps artillery preparation and accompanied by infantry. His tactical modification was leading with the Matildas instead of the infantry, but it would all look quite like a Battle Group or brigade attack today. Because the British were able to attack the Italian strongpoints sequentially, the full weight of Corps artillery was available for each attack. Each attack was followed by deliberate sustainment operations for the Matildas to ensure that they were able to get to the next fight. So not very ad-hoc.
The assault on Bardia was preceded by three days of naval gunfire (by three battleships) with over 160 guns from Corps Artillery firing together in support of the break-in. Methodical, meticulous warfare. There was certainly adaptation and improvisation on the ground to account for friction, but this was a deliberate Corps operation.
There were some more ad-hoc groupings for the forces that established the blocking positions to trap the retreating Italians at the conclusion of Operation Compass. "Jock Columns" were used by 7th Armd to guard and demonstrate in support of 4th Indian Divisions assaults on the initial strongpoints and for the subsequent assaults on Bardia and Tobruk. So they were useful, but the real success story was deliberate combined arms with tanks that the Italians had no answer to as the special sauce. Add to that facing a foe in the desert that had no real mobility. None of this takes away from the creativity of O'Connor in his plan, nor from his boldness throughout the campaign. He was willing to take chances in pursuit and this paid-off at the end of Compass. Later 8th Army commanders were not quite as willing to pursue with as much vigour.
The British would be on the receiving end of a similar calculus over much of the same ground when they faced an opponent with a ready answer to Matildas that could execute combined arms at an even higher level.
Back to Canada and the modern day, there is value in having forces that can conduct security operations. A screen provides warning, a guard provides time but operates under the support of the guarded force while a cover protects the covered formation independently. Guards and Covers will almost always have combined arms, with a Cover likely having its own artillery. In a Brigade context, though, you will see Screens and Guards. A CMBG could be a Cover for a higher formation. I think Cavalry is an unfortunate term to use because it unpacks differently for different people.
UAS have absolutely made an impact in security operations and information gathering. Any reconnaissance organization should have some UAS. I think we need to be careful, though, looking at the use of UAS in fairly static battles and making sweeping generalizations about all operations.
