Elizabeth Burton (Paulet) - William Burton, Lord Burnell

It appears to be only weakly sourced online. Anyone care to defend William's parentage with reliable sources?

Elizabeth is with this spurious relationship daughter of Roberts sister.
Really suspicious.
Husband / uncle: Robert Burton
Mother of Elizabeth and sister of Robert: Margaret Paulet

Does anyone have any historical proof William Burton actually existed?
This tree also completely misses that Robert Burton was married to Elizabeth Bykebury (Bigbury) the daughter of William Bykebury (and Elizabeth Paulet's 1st husband.)
Robert & Elizabeth Bykebury had a daughter Elizabeth. Both the Elizabeth's (wife & daughter) died before Robert & Robert then married Elizabeth Paulet. There is a belief that Elizabeth Bykebury died circa 1460 & therefore Elizabeth Paulet would have been too old to have issue with Robert Burton.
Has anyone studied the IPM of Robert Burton?
Also, this William Burton is all over the internet but no one can decide if he's Lord Burrel, Lord Burton, Viscount of Burnell. Why is there no historical record of him or his title? (How do the Burrells feel about him being Lord Burrel & where is Burnell?)