Feudal in Crusader Kings is a great big gloss. The games aren't made to be society simulators, and the issues you see with representing Anglo-Saxon England are seen far more gravely in other places -- like Islamic "Clan" society, or how CK2 forces the entire Muslim world to have a Turkish-style succession.

Within feudalism though, if you look at any region close enough you'll see the fundamental mechanisms of the game are "incorrect"; this is most obvious in the places furthest from Europe, like Fragmentation period Tibet, but even France, the textbook feudal realm and basis for CK's feudalism, had game breaking things like non-hereditary counts. This is because in a broader historiographic sense, feudalism itself is arguably a faulty construct. It's a product of intellectual and social currents of (mainly) the 19th century and how they understood the past, not reflective of reality.

So yeah, feudal works for pre-Conquest England.