I was impressed first by the fact that whoever designed this particular Lisp system cared about efficiency.
This isn't a particularly unusual approach. Common Lisp, a contemporary Lisp dialect, was designed with efficiency in mind. The approach of "Lisp = slow + inefficient + spending 80% of time on garbage collection" is a myth.
This comment was regarding TCO, which Common Lisp (unlike Scheme) doesn't guarantee. Many CL compilers today offer it, but IIRC that was rare in the 1980's.
There was also a lot of consternation when TCO was formalized as part of R*RS. It's a fundamental part of how Scheme works, so it was obviously necessary. But from a compiler writer point-of-view, it was a rather exotic demand at the time.
Though we've moved from a period of languages as defined by a spec to languages defined by implementation. Such as Perl, PHP, Ruby and Python. So what is "normal" has changed a lot.
Not really. If you were at MIT in 1983 then one would have probably access to Maclisp, whose compiler had seen some work by then. The first Scheme implementation was also written in Maclisp.
This isn't a particularly unusual approach. Common Lisp, a contemporary Lisp dialect, was designed with efficiency in mind. The approach of "Lisp = slow + inefficient + spending 80% of time on garbage collection" is a myth.