No the higgs mechanism was directly proposed from how particles masses were not explainable from the existing model -- so it's clearly in the "surprising observation" category.

The positron was, "oh what if we had this thing that is mathematically possible". Very different. IIRC the discovery was kind of independent. It was in the data the whole time so if the physicists didn't just ignore those "impossible" bubble tracks they might have found it before the math.

If we discovered superluminal tachyons that would definitely count. But we haven't found those.