The point of the Germany build was that it didn’t give you a clear indication of their plan. Full artillery does: that they’re (probably) going east. Full mech/tank does: that they’re (almost definitely) going east.
Yes, the most effective UK full defensive buy is all infantry, but the fighter is useful for the rest of the game, and that buy is still a very, very strong sea lion deterrent. It’s more common than all inf.