Mims head and Invincible were ultra rare for their time. There wasn't posses of people riding them around. 0lights was the only drop for Mim's head in 25. Thats 25 weeks of farming 0lights. Not that many folks did that. Same with invincible. Maybe 3 or 4 a raid group (average) for Invincible. Shadowmourne was easy to get but, not as easy as say the the FL staff. So it isn't like a ton of people can even "1 up You" in that sense.
I wouldn't be ashamed. I'm on like week 150 for a horse from Kara (thanks to running it all of BC and loosing on it twice) which I've been farming a long time. I've got a decent amount of TK kills as well still no mount. I'll be just as excited to get em and just as proud of em as if I had gotten them the first week in there.