Tintagel’s true scale wasn’t understood until the 1980s. After centuries of denial, a drought led to a grass fire so intense it burned away the apparently thin turf covering over 200 ruined buildings. No one had noticed them before. :^)
If indeed there was a King Arthur, it’s more likely that every distorted piece of folklore referring to various post-Roman local lords (Romano-British at best, probably) wound up grafted into a single quite recent (15th c) legend.
Vortigern was historical, and probably wasn’t rival or archenemy of Arthur, but formed a good bit of the basis for the King Arthur composite. There’s actually a very old medieval burial monument in England (a part that used to be Wales) that states that the historic king buried there is a descendant of Vortigern.
Another part of the composite seems to be Magnus Maximus, a 4th c Roman governor of Britain who also vied for the emperor’s job, went to the mainland (as one story has Arthur doing), and died in battle trying.
Even in what is now Scotland there’s an Arthur’s Seat, which probably has nothing to do with the rest of the legend and was given the name much later on.
https://en.wikipedia.org/wiki/De_Excidio_et_Conquestu_Britanniae
https://en.wikipedia.org/wiki/Category:Arthurian_literature_in_Latin
https://en.wikipedia.org/wiki/Nennius
https://en.wikipedia.org/wiki/Matter_of_Britain
https://en.wikipedia.org/wiki/Vortigern#Pillar_of_Eliseg
https://en.wikipedia.org/wiki/Geoffrey_of_Monmouth
https://en.wikipedia.org/wiki/Chr%C3%A9tien_de_Troyes
https://en.wikipedia.org/wiki/Welsh_Triads
https://en.wikipedia.org/wiki/Mabinogion
The name Camelot appears to have been taken from Camulodunum, the Roman name for modern Colchester, and their provincial capital. Probably was invented for the relatively modern Arthurian legends.
Mary Stewart’s take on it (if memory serves) was that it was built along the River Camel. The better known one is in Cornwall, but there are streams that are called rivers known as Camel, apparently.
There’s also the River Cam that flows through Cambridge, so the name Camelot would mean something like Ford of the Camel.
Geographically Cambridge is more centered in the apparent core of a post-Roman realm which had Hadrian’s Wall on the north, so-called Offa’s Dyke on the west, the Wansdyke on the south, and the Cardyke — a Roman canal — either as its east frontier or the core of the polity.
https://wikishire.co.uk/wiki/River_Camel
https://wrt.org.uk/project/river-camel/
https://www.wadebridgemuseum.co.uk/river.html
https://en.wikipedia.org/wiki/River_Cam
https://peterborougharchaeology.org/car-dyke/
http://www.lincsmag.com/Lincolnshire/001_LINCOLNSHIRE_ROMANS_Bruce_Barrymore_Halpenny.html
Britain’s oldest canal in Lincolnshire is up for sale
https://www.bbc.com/news/uk-england-lincolnshire-48908186