Two/three thing come to mind immediately. What are the 'new playthings'? Certainly not the existing guns that are actually in warehouses. The 2pdr was movable, but was also 150% heavier than for example the 47mm Bohler, that was every bit as good (or bad) hole puncher as the 2pdr, and was could fire a bigger HE shell. The 47mm from interwar tanks will be punching holes in German tanks of 1939-40 every bit as good the 2prd, and 3pdr Vickers will do even better.
As for criticysing the 3pdr for having too small a HE, and then go with 2pdr instead??
These matters would have to be addressed to the decision makers at the time. I don't justify them, only describe their line of thinking as I understand it. When the 40mm 2 Pounder was put into production the Germans and Americans were choosing 37mm guns.
17 pdr was not too big and certainly not too powerful for tanks, it was indeed a thing where British tank designers and brass botched the whole turret/gun equation. Design a turret, and then discover the gun won't fit??
Purpose of a tank is to carry a worthwhile cannon, and British made mistakes when going down from 6pdr of ww1 down to 3pdr in interwar period, and again down to 2pdr.
Everyone went down in calibre post WW1. The gun/turret mismatch was the fault of separate requirements for each and not a single unified requirement. Vickers were asked for a HV 3" gun specific to tanks. The turret designers were asked for turrets to take existing production. Both did adequate jobs: only separately. Cock ups occur all the time everywhere. The mystery is why it was so long to fix it. Probably because the existing gun went to a 75mm barrel in the same gun and gave adequate infantry support HE for the moment. Overlord was in the offing and Cromwell production lines could not afford a delay. Cromwells were getting all the QF75mm guns that were being made a the time. The standard 17 Pounder is a beast of a gun to squeeze into an existing design. Just look at the improvised Firefly with it's weird fixes to force the thing in the turret without it hitting the rear wall or killing the crew on firing, all in the space that would be ergonomically inferior to a poorly made gibbet. I have been in one and I still wonder how I got out with all my limbs and minor projections. The infantry mount reduced the forces on the mounting by allowing a long recoil movement which let it have a lighter mount. Despite which it was a nightmare for infantry to move about once released from it's tractor. Thus we can see the OTL 17 pounder WW2 tank, the Challenger, needed a larger hull and high turret to let the 17 Pounder fully recoil. The issues of turret ring diameter, often quoted, are rather thrown aside by the Charioteer which mounted the 84mm 20 Pounder on the Cromwell turret ring. Albeit with only small arms/shrapnel proof turret armour. There was a good reason why the Germans did not put an 8.8cm in the Panzer IV. Like the mismatched Cromwell/Vickers and Comet it could only fit a 75mm size and weight. Had the Vickers/[Cavalier/Centaur/Cromwell/Churchill turret designs] worked then the 17 pounder would have been superfluous in a British tank and the same production lines would have been pouring them out continuously for the last 3 years of the war with only minor changes.
There was the RR Kestrel around, tooling and all, before 1939. Not needed for ww2 use, trainers can use Mercury.
Actually the Kestrel tooling went over to Merlin and Vulture production by and large and the early war Mercuries were in demand for operational types so the remaining Kestrel stocks and spares supported trainers. Lord Nuffield should never have been allowed to make his Liberty variation but should have been forced to make the existing tank specific Meadows and/or Bedfords.