Though I agree with you over his progression, he's learned a number of tricks within Getsuga (only that they aren't pronounced yet, if ever)-- he can hold the Getsuga within his sword (bankai) and swing the sword around with it like a ghetto lightsaber; (Ulquiorra mentioned this), and before that he learned how to split the force of it into two beams (if I remember correctly), and he can also use it to temporally shield himself from an oncoming blow (Ulquiorra mentions this to Ichigo, after he releases and attacks him).
Though Ichigo only "knows" Getsuga Tenshou, it's no longer a One Trick Pony, as he learns how to use it more offensively and defensively.
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