> This idea that researchers should be teaching is just horrible, they're not significantly overlapping skill sets.

It would seem so, but you have to be careful
because too frequently the claim is badly false.
Let's consider courses in your college major
from junior year or later (and there can be other
cases, e.g., for advanced students who get into
serious material before their junior year).
Reasons:

(1) It's a big, often bad world out there
with a lot of dumb, badly adjusted,
sick, injured, confused people. One way
academics filters whom they let teach is by insisting
on some research accomplishments.

(2) To do a good job teaching (in your major,
junior level or higher) there can be
challenges in understanding the material
really well, that is, the details, done
well, an overview, balance, judgment,
synthesis, bigger picture, important
connections with other parts of your
major, applications, research, etc.
So, for this level of understanding,
it can be important for you to have the
brightest, most knowledgeable prof
you can get. That is, a less
bright, less knowledgeable prof
may not have such understanding
themselves.

(3) One thing, on a good day, you
might get in a classroom,
face to face with a good prof is
an example of how he thinks. There's
a lot of junk that can find its way
into thinking; it can be a real surprise
to see, from a really bright prof,
how he manages to filter out all the
junk, set aside the not very
good content, and keep the best
content. Once as a graduate student
I heard a lecture
by S. Eilenberg, and afterward
a junior prof said: "He sure doesn't
waste time with little ideas.". That
could be a good remark to hear. You
typically won't get good remarks of that
kind from profs who are able to teach
the material but don't bring a lot more
into the classroom.

(4) Actually, in some fields, starting at the junior
year, you can begin to notice that
"it's a small world". So, if you have a
good researcher as a prof, then you can
be surprisingly few connections from the
best people in the world in the field;
not good to miss out on that.

(5) Yes, it's important to learn, but, really,
from the junior year on in your major, there's
often some question about just what and how
much you should learn. Or, yes, in K-12 and
the first two years of college, the emphasis
is on the student learning. By the junior
year, the lesson, quite clear somewhere
in a Ph.D. program and starting
to become clear in the junior year, is that no one can
carry all the research library around between
their ears. So, a big question is, since
you will be learning only a tiny fraction
of everything in the research library,
what fraction should you learn? One
path to a good answer is to have a prof
who has, from his research, a good
view of the future of the field
and can use that view to help
select and weight what to present
in the course. That is, it's easy
to waste time on junk, trivia,
less important material, dead end
detours, etc., and a prof who
does much of that can't be good
at research.

(6) This stuff about bad teaching is not
a small problem. Instead, it's far too
easy for academics to fall into some
rigid nonsense such as in some of the
stories about teaching in Asia --
nose to the grindstone, shoulder to
the wheel, ear to the ground, dot all the
i's, cross all the t's, but still don't
have even a weak little hollow hint
of a tiny clue what the material
is about. E.g., recently here on
HN is a link to the famous Feynman
description of teaching in a country
in South America. It's too easy
for the nonsense Feynman described to walk in and
take over. The peer-review process
in the better journals tends to
cut out that nonsense.

(7) In some majors, it can be important
for you to meet people, hopefully via
your coursework. A good researcher
well known around the world might
give you some introductions that
could prove priceless.

There's more: Broadly a big issue is
quality, and there's no easy substitute.

One response, at one time common at Courant,
is "If you just want to learn the basic
material, then don't bother with classes
and, instead,
just get some books
and study."

At one time the Web site of the Princeton
math department said, (from memory, likely
not exactly correct): "The courses given
are introductions to research by world class
researchers. No courses are given for
preparation for the qualifying exams.
Instead, students are expected to
teach themselves such material.". So,
by the junior year, a course should
have more to offer a student
than just the basic material
a good student could just get from
the books.

Education is about the future,
preparing to do well in the future.
As from character Yoda
in Star Wars, "Always difficult
to see, the future.". Yup, he
was correct. Good researchers
have some advantages in
seeing what is more promising
for the future.