I got them all, and have never tried to get those which require the MGGS with any alt. The one on Alderaan took me mostly just a while to find the spot that was working (and even then I had to climb the ladder, which I heard was removed, because it was not supposed to help to get up there). The Corellia one took forever, and I even died a few times, because I ended up falling instead of getting there. The one the fleet was the one where I simply got pulled up by an sage, so had no trouble there (eve though I know that many complain about it). So, not a single one of them seems to really work.
use a skill like [take cover] [force sweep] or any other ability you can activate without a target, and it will stop your movement, which is a useful way to help you land where you want. Not too sure what your issue on corellia is. I never had issues there. For the republic fleet datacron there is an issue but the above method fixes that.