Well... Namor obviously became anti-nazi and anti-Japanese because his writers were, and they wanted to write wartime propaganda stories, but the change was still a gradual one, and I never felt Namor was really out-of-character during these wartime stories. Also, remember we're only getting a few stories from all over the timeline in the Masterworks currently - it's a bit hard to follow character growth this way.

Out yonder, under the shining vault, among men the saying goes: 'Man, be thyself!'
At home here with us, 'mid the tribe of the trolls, the saying goes: 'Troll, to thyself be-enough!'