I found that some groups of letters in math mode have strange spaces:
$\Delta XYZ$
, $\Delta WZU$
looks bad, but some others like
$\Delta STU$
look fine:
I found that this is not a problem of italics:
I tried it in pdfLaTeX, LuaLaTeX, XeLaTeX and also Overleaf - the result is still the same. How can be this "unnatural" space removed?
\mathit{WZU}
etc., to get something like more like normal "word" spacing.