I agree with this estimation of you F-14. I think that, with all the suffering it caused, the big earthquake in the first movie also is in part responsible for the uniting of the different kinds. According to LBT 7 the older dinosaurs did migrate to the Great Valley together, same as Littlefoot, Cera, Ducky, Petrie, and Spike did (something that was not suggested in the original movie). If they decided to stick together in spite of their earlier racism, the earthquake is likely to be the reason. Herds and families had been torn apart and in such a hostile country it may have been saver to wander in such large groups as to scare away sharpteeth from attacking them (on the other hand it remains a mystery how they found enough food to sustain such a large herd).
As for the racism of Littlefoot's mother, there is one important difference between her racism and that of Tops. While she accepts the racism because "it has always been that way" (so just like Ali she probably never knew anyone but other longnecks), Tops seems to adhere to that racism for conviction of the own superiority. He is less ready to learn than Littlefoot's grandparents are (and than his mother would have probably been).
When Littlefoot asks his mother for the reasons why the different kinds should stay apart from each other she evades the question she puts him of with the prospects of many longnecks to play with in the Great Valley.
If Cera had asked her Dad the same question she would have most likely been given a lecture about how much better threehorns are than any other kind.
As for Tops as a father he seems to be very much overstrained with the task. We know nothing about Cera's mother, but it is possible, even likely, that Cera's bringing up would have been very different if she had been around too. I am not suggesting that her mother would have been less racist than Tops, but I suppose there wouldn't have been so many scenes in which Tops was just perfectly helpless about what was the right thing to do.
We don't know about the past of Tops and Tria (they apparently had been very close friends before Tops met Cera's Mum) but maybe her kind and compassionate nature was one important point in her becoming the mate of Tops. Some people really fall in love with others as they feel they can help them. Maybe Tria felt a great appeal in the idea of helping to "heal" the torn up family of Tops.