In any languages with multiple namespaces, anything inhabiting some non-primary namespace (i.e., not the matrix containing normal variables) feel second class. Emphasis "feel", and hence "awkward" over "technically limiting".
Additionally, it makes the transition to lambda calculus more difficult to grok, which somewhat hinders understanding. It's pretty trivial to make some simple rewrite rules from (most of) Scheme to lambda calculus: it's a two-hour project at most. Doing this for CL is much less intuitive/elegant, possibly making it more difficult for those with that sort of theoretical background.
Additionally, it makes the transition to lambda calculus more difficult to grok, which somewhat hinders understanding. It's pretty trivial to make some simple rewrite rules from (most of) Scheme to lambda calculus: it's a two-hour project at most. Doing this for CL is much less intuitive/elegant, possibly making it more difficult for those with that sort of theoretical background.