That was, as you note a trials weapon. The ACIII was designed with the 25 Pdr in it's turret.
The twin-25Pdr vehicle proved that it could take the recoil from the 17 Pdr gun on that sized turret ring. Interestingly, the report from that trial found it's way to the UK and directly influenced the design and development of the British Firefly tank. Until then, they hadn't thought it possible to mount such a powerful weapon in the Sherman.
It took the British Army two years of trial and error to develop the use of artillery to the extent that it basically won the Western Front for them. An artillery bombardment wasn't new. What was new was a marching barrage to convey the infantry (and armour) onto and over the enemy position. It was considered better to hug the rear end of the barrage and if necessary suffer casualties as a consequence than to fall behind it and allow the enemy to emerge from his dugouts and mount the trench firesteps again.
Until 1945 the British Army was more interest in forcing the enemy to take shelter and be neutralised that way than to destroy the enemy. The US Army was more interested in destroying the enemy with it's field artillery hence the difference in calibres with 25 Pdr being 89mm and the 105mm calibre. This has since become merged with 155mm, with the balance going at the Americans' insistance to destruction over neutralisation. In 1945 the Royal Armoured Corps carried out an experiment where they deliberately drove a squadron of Churchill tanks into the beaten zone of a 25 Pdr battery. The Churchill's basically emerged unhurt (with except for a few aerials broken/removed).