They don't necessarily have any ability to pay, which is the scenario that brought prop13 to life in the first place (low-income grandma kicked to the street by taxes).
Someone of modest income who bought a modest 100K house years ago isn't cash-flow rich today just because the paper value of their house went up. They are probably retired living on a small social security check and don't have much any ability to pay, let alone the "greatest ability".
It's fine to have different views on how society should handle this tricky scenario, but let's be intellectually honest with the core facts.