“Compare how similar the baalei tosafos are with each other, as opposed to with the Chachmei Sefared, for instance, and vice versa. Also, you’ll never find a talmid always agreeing with his rebbe, and those differences will be magnified in each subsequent generation, especially when there were multiple rebbeim. Still, the relative similarity still speaks of an oral tradition.”
I think the similarities are not so much in their pshat in a given instance (where there is often disagreement with Rebbeim) inasmuch as a similar methodology (where they are similar to their Rebbeim as contrasted with the Chachmei Sefard).