Would you ever know more about a person by reading their 4 letter type than by reading their MBTi test answers? No.
Um, sorry, but not to put too fine a point on it, you're just
wrong.
As the leading Big Five psychologists long ago acknowledged, the MBTI dichotomies are tapping into four of the Big Five dimensions — and those are substantially-hardwired clusters of personality characteristics with respect to which
identical twins raised in separate households are much more likely to match than less-genetically-similar pairs.
In order for the items on an MBTI or Big Five test to do a reasonably effective typing job, there's no need for them to come anywhere close to
covering the waterfront in terms of all the ways those hardwired preferences — not to mention
combinations of preferences — can affect someone's personality, and they certainly don't.
To just take introversion as one example: psychologists have been studying introversion for decades. Is it really your understanding that when the MBTI types someone as an introvert, we don't know anything more about them than the specific stuff in the E/I items on the MBTI test?
If you're interested, you might want to check out
this TC Wiki article (already linked to earlier in this thread) for more about the reliability/validity/etc. of the MBTI, and how it relates to the Big Five.