Buddha, I suppose you're right. Though how do the particulars of pure lands relate to those Mahayana doctrinal things?
And I've heard a number of explanations of pure land practice, ranging from something akin to a meditation object as you've said to devotion to literally, asking to be let into whatever-land. Apparently pure land practice often was/is combined with other practices, so I suppose a number of adaptations and approaches have sprung up.
I won't lie and tell you I know a whole lot about this, but it's kinda interesting.
I can't say I know it too well myself. Maybe Ven. Paññāsikhara will step in to help us out here. But meanwhile let me give it a try.
Buddha contemplation is a way of realizing our own buddha nature. While you are thinking of Buddha, your mind becomes Buddha mind. While the Pure Land can be conceived as external, it's also internal. Calling on Amitabha can be seen as an aid or expedient which helps us realize our innate potential.
Buddha nature, meanwhile, is related to sunyata. Realizing emptiness, in Mahayana, is considered the key insight that leads to attaining buddhahood -- which, in turn, means that one has cast off all clouding defilements and realized one's buddha nature. When we access our buddha mind we are apprehending emptiness and transcending all dualities, including of course the duality between Amitabha (as an external object) and ourselves (the person calling on Amitabha).
"Mind only", which has its roots in the first few verses of the Dhammapada, teaches that the mind creates its own reality. An impure mind surrounds itself with impure things and a pure mind surrounds itself with pure things. A mind that is focused single mindedly on Buddha will thus be reborn in the appropriate state -- i.e. a Pure Land.
I'm no doubt mangling this terribly but do you see how the concepts inter-relate? (dare I say "inter-be?"). Mind only=Pure Land=Amitabha=Buddha Nature=Sunyata=Causes and Conditions=Mind Only...