Yep, and I agree with you. One funny thing I've learned from my conversations with some Catholics is that to be called a heretic by them is actually the second best thing to be if one does not believe in Apostolic succession. :) That is, (and I invite Catholics to comment) I don't think they would call an LDS a heretic because they don't merit the level of heretic. :)
Ping to 1551.
In order to be a heretic one has to be informed of the true faith, and then reject it. A Buddhist or, possibly, a Mormon is not a heretic, he is someone of a different faith. Protestants are heretics insofar as they understand and reject Catholicism. Since 20c Protestantism does not seem to even understand itself any more, I hesitate to apply the term to latter day Protestants. They are simply confused people, no comment on the present polite company.
I don't think there's going to be a universally agreed upon taxonomy of deviations. Dante considers Mohamed a heretic - which probably reflects the thinking of his time (1300's). I would think LDSers would be heretics, just in a whole lot of different ways. I dunno though.
We will use the word "heresy" for a line of thought or a doctrine, but a heresy can be held in error rather than stubbornly.