Custer screwed up - big time.
That’s too easy an answer. It’s far more involved than that.
I know.
Not to say that statement is wrong, but consider this, for a moment:
Custer did have extensive experience against the Indians.
In all previous encounters the Indians had displayed the same tactics:
Hit-retreat-hit again.
The Indians realized this plan was not working.... they changed tactics.
LBH was the first time the new tactics were displayed: Combining tribal forces, going on the offensive and not retreating.
To say Custer "screwed up" is simplistic (and I do not mean that offensively against your comment) but for Custer to have proceeded otherwise, would mean he would have had to anticipate the changed tactics of the Indians.