That's one of the reasons LBT XI has got to be my least favorite of the series...the characterization of Mr. Threehorn and Big Daddy is just no good. But, hey, I guess that's to be expected from the movie that gave us a song about how dads stink! 
Glad to know that I am not the only one who thinks XI is the worst. XD Coupled with that Littlefoot's lies, Topps snapping at Tria, and Littlefoot going "who needs friends" are my most disliked moments in the franchise… So this movie has the worst moments, worst characterization, and the worst dads. I see "worst" written all over this. 
Ha! Exactly.

XI had Topps, who was already hard to like, become even more unlikable...but as you've brought up, the worst offense that movie committed was
Littlefoot. WHAT were they thinking? Except for getting food for the Tinysauruses, Littlefoot was such a selfish jerk through that whole movie. I'm honestly surprised that XIII is more of a least favorite in the fandom than XI...yeah, XIII was weird, but at least it kept the main character's personality intact!
If you ask me, the only good thing XI brought to LBT was Tria. And I have to say, the way they brought her in there was pretty cheesy, being so lovey-dovey over Topps with not much more backstory between them than "we know each other!" I really liked Tria in XII and the TV series, though (that scene where she's afraid Topps is going to roll over on the egg was hilarious), so I can overlook her XI introduction, I guess.