The problem is mainly the square brackets that force one to go through strings, in my experience. Can't build something like "set foo [cmd $bar]" purely by using [list ...] shenanigans, since list will quote stuff you don't want quoted.
True, I believe I mostly worked around that limitation by splitting off quoted from unquoted code into separate commands. So in your example "[cmd $bar]" would be in a separate unquoted command, probably putting it in a temporary variable, which can cause problems as it's hard to have a private scope when doing metaprogramming. You can also use "[list]" in the middle of code, but it gets more error prone, for example "set foo \[[list cmd \$bar]\]"
For sure there is a lack of proper "code as data" constructs in Tcl, like you would find in Lisp.
Actually, you can see the "backslash hell" version here if you want to estimate the clarity gains: https://git.sr.ht/~q3cpma/tcl-misc/tree/f613898c3dcfa3ca958a...
I also had further fun with wrapping "proc" by implementing a "pyproc" which called out to Python while looking like a normal Tcl proc.