Using document level function to call different code level functions

test.tex

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\cs_new_protected:Npn \johannes_all_caps_kern:nn #1#2
 {
  \tl_set:Nx \l_tmpa_tl { \tl_upper_case:n { #2 } }
  \group_begin:
   \addfontfeature{Scale=0.9}
   \textls [ #1 ] { \l_tmpa_tl }
  \group_end:
 }

\cs_new_protected:Npn \johannes_all_caps_nokern:nn #1#2
 {
  \tl_set:Nx \l_tmpa_tl { \tl_upper_case:n { #2 } }
  \group_begin:
   \addfontfeature{Scale=0.9}
   \textls * [ #1 ] { \l_tmpa_tl }
  \group_end:
}

\NewDocumentCommand \allcaps { s O{200} m }
 {
  \IfBooleanTF { #1 }
   { \johannes_all_caps_kern:nn { #2 } { #3 } }
   { \johannes_all_caps_nokern:nn { #2 } { #3 } }
 }

\ExplSyntaxOff

\begin{document}
\end{document}