I did not know that, but I always sensed that Marshalls were not as heavily built as some other cabs. There are all sorts of reasons why one would or would not choose a certain material...type and size....for a cab.FYI, 15mm (5/8") is the standard size Marshall has used since the '60s 4x12 cabs.
I think it's more than proven itself given the sheer number of Marshall cabs still kickin around the globe.
Because you like 410s better than 212s?Vintage 'drip-edge' Princetons were seemingly built with very cheap materials and they sound great. I have a home-made 4x10 where I used open back 3/4" Birch and I have a THD 2x12 which is a lightweight ported cab. My homebuilt sounds better. Sounds amazing. But I have no way of explaining why.