A BELIEF is inherently of questionable validity; not necessarily untrue, but not definitely true, either. If found to be untrue, one's mind can be changed
If something is indisputably true, it is a FACT, not a belief.
DELUSION is an unshakable belief based on
FALSITY, not fact.
FAITH is a belief if it can be amended if warranted; a DELUSION if it is unshakable.
But, belief in, faith in, God cannot be proven or disproven, as either true or false, so it cannot be a DELUSION.

I would prefer two other definitions
BELIEF
A conclusion reached that shows it can further be used to establish other conclusions in a cohesive or logical manner.
FAITH
A belief without evidence.
(Simplicity Rules)

Relevant beliefs of my own. Faith is a necessary human device to allow normal living; Faith can exist outside of religion but because it questions the need for evidence its use has diminished religion and the people who use that word; I would much rather they stuck to using only the word religion and not use 'Faith' as a substitute for 'religion'.