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The weight limits on tanks usually had little to do with combat capabilities, except for power to weight ratios with available engines ( more on that later) and much more to do with transportation and general mobility. Mobility in the sense that if the majority of bridges in the area you want to operate in are only rated for 20 ton vehicles a 22 ton tank is a gamble, a 30 ton tank probably won't make past the the first couple of rivers. What is the capacity of the tactical temporary bridging equipment if the existing bridges are blown? Weight also governs the number of available railway carriages and even the docks (cranes) that can be used for sea movements.
There are reasons that some weight limits were what they were before the shooting started and why some bigger, heavier tanks stayed limited in production.
The Liberty was a bad decision. It had a very troubled reputation as an airplane engine. a good Liberty wasn't a bad engine but a bad Liberty was a disaster. Many of the WW I Liberty's should have been melted down while brand new. Anybody who thought this was a good choice in 1937 must have been looking at the bottom line (cheap).
Personally its my belief that the main problem was the basic tank. The PzIII originally had a poor gun and thin armour, in a stand up fight the Matilda had most of the advantages. But what the Pz III had in spades was growth potential.
The british started the war with the Matilda and there was nothing wrong with that, where they went wrong was designing the Valanine. They should have designed it with growth potential so as the 6pd came on stream they could have installed it, in the same way the Pz III was easily upgunned from the 37mm to the 50mm L42 and 50mm L60