The British had one of the best tanks in the world from 1930 to 1940, except the British military didn't use it.
The Vickers 6 Ton was better than its competition, and was the basis for the Polish 7TP and the Soviet T-26.
It could be considered that the failure of the British to adopt the Vickers 6 Ton, and then to develop it, lead to the virtually useless British lights of the early war years. It could have been adapted for either the 2pdr or the 3in CS howitzer, and would have been useful in France and some of teh early desert campaigns.
Give the BEF a full complement of Mark III's and IV's and have it led by clones of George Patton and Erich von Manstien and it is still going to be driven back to the Channel. Nor would it have made much of a difference in North Africa until the British built up the logistic backing to continue an advance past El Agheila. Yes, better tanks and generals would have helped. For that matter, early adoption of jerry-cans for petrol would have helped in Africa too. That won't change the fact that the British needed a much better French Army in 1940 to stop the German advance through Belgium and that they were constrained by logistics in North Africa in 1941-42.