The problem with landing in Alexandretta was that it was in the French sphere of influence and they were opposed to the British landing there. It appears they went ballistic when a RN ship landed a raiding party and blew up a train and some buildings. Sean McMeekin talks about in his book, the Ottoman Endgame. Strategically, it was an excellent place to land and it would cut off the Ottoman armies in Syria/Palestine, Mesopotamia and Arabia. While it wouldn't open a passage to Russia, it might have knocked the Ottomans out of the war much earlier.