Imagine what would happen if you used early Cold War AT and AA weapons against a force equipped with tanks and planes from the First World War. We already have the technology to make decent portable AT weapons that would be excellent against these modern men-of-war: https://modernfirearms.net/en/sniper-rifles/large-caliber-rifles/austria-large-caliber-rifles/steyr-iws-2000-eng/ Power armour isn't even on the drawing board yet, and we already have something to counter it. You'd have to develop and test to the point all the teething issues are gone, then equip your infantry en masse, and hope that the doctrines you came up with will work on the field.