#6 My answer in #4 ...
See my answer in #1.
Why all the discussion? The established phrase just is 'wide of the mark'.
And who says it's an old spelling mistake (#5)? Compare 'the arrow fell short of the target'.
Note that English 'wide' doesn't primarily mean 'far'.
Personally, I visualise 'wide of the mark' as 'some distance to one side of ['of' again!] the target'.
See Shorter Oxford Dictionary, 1975 edn.: (my bold)
III,3 Deviating from the aim, or from the direct or proper course; missing the mark or the way.
a (lit[eral]); spec. in Cricket, of a ball bowled too far aside from the wicket [...]
b (fig) (a) [...]
(b) Const[ruction] of, from (now rare or obs.): esp. in phr. w. of the mark 1566.
5. At a distance to one side; aside from the aim, or from the direct or proper course 1534.
A ball ... pitched a little wide of the off stump 1833.