iMessage definitely has more hooks in than those listed. It’s an integral Apple service that’s hooked into your deeper iCloud account. And because of that, they know a lot more than just a mere “chat” app would get access to. Which likely makes it harder to quantify.
Moreover, Meta and Alphabet also cross reference a lot of data points from all the other sources they have (cookies, IP logs, etc.). Again making actual data points fuzzy or incomplete.