I wouldn't say Bron is heartless. You have to remember didn't recognize Littlefoot when he first met him, so he more than likely doesn't know about his son's journey to the Great Valley. Sure, Littlefoot may have told him everything while they were in the crater, but it would have happened off screen. Another thing to think about is that the journey to the Great Valley wasn't a test to see if Littlefoot could lead a herd. It was test to see if he had what it takes to survive. He obviously failed as a leader because the group end up abandoning him. Sure they all found the valley in the end, but still a true leader would have kept the group together at all times and listened to the input of his/her group members.
1.) Littlefoot was only 5 years old then.
2.) He was going the right way. He doesn't have the ability to
force the others to go with him.
3.) It was Cera that was the bad leader. She thought she was so high and mighty and was so stinking proud, even after being found to be wrong. She nearly got them killed. They
would have died in fact, had not Littlefoot gone after them!
A good leader would risk his own neck when his followers get sidetracked and go into danger. Littlefoot is the opposite of Pterano, and, indeed, Cera.
I think that, say there was a vicious Sharptooth coming and one of the Gang of Five got tangled in a vine and needed to get out, I could see Littlefoot actually staying there until his friend was freed or them both going down together. He might tell others to save themselves if he is the one caught in the vine and not to risk themselves to save him, but, if it's a friend in danger, he will do all he can to save them and will not go off to save himself, even if the friend is actually yelling at him to do so.
As for Shorty being afraid of Ruby, why should he be? The only meat she eats is shells and maybe fish. It's not like she is having lognneck steak in secret.
As for Chomper, if you recall, Bron said that he'd been there before. Shorty likely came too as Bron's adopted son. If so, he may well have met Chomper before, did an OMG before, and hence gotten it out of him earlier.

Chomper's eating habits bug him (pun maybe intended) though they shouldn't, as we all know what our friendly neighborhood Sharptooth
could be eating, and that part still likely does, even if he's gotten over Chomper, er, somewhat. Perhaps Shorty is still a bit shy about being around a Sharptooth with no adults around. Shorty still appears to be kind of a headstrong, kind of Cera-ish. (Cera is a nice character, but she's hard-headed and that cannot be denied and she can be a bully at times.)