Not so! If you understand The Basic Rule in op-amp circuit
design, you'll see that there is no difference among these
applications. Nor will you be wondering how to do something.

No, you only "get" to that point with experience. There
are different design issues involved in each of the above
applications. If you understand how an op amp works
"in theory", you can look at an EXISTING circuit and suss
out the functionality that the op amp is providing. But,
that doesn't mean that you would be able to come up with
the particular circuit topology that is avoiding some
particular *real* (vs theoretical) limitation of that
*particular* op amp and/or leveraging some particular
characteristic thereof.

If it could all be boiled down to a simple rule, then
EVERYONE would be able to design perfect circuits "first
time, every time" -- with/without SPICE.

I want to design a 2KW, 2KV SMPS and use an op amp to
compute the error term. Should be no different than
designing a pickup for an electric guitar, right?
Should I expect to have either/both of those designs
on my desk, this afternoon, *completed*??

I probably overstated the case, but understanding Basic Principles can be a
major leg-up to creating a workable design.

A person who doesn't understand The Basic Rule of Op-Amp Circuit Operation
is going to have a lot of trouble.

I might add that, several years ago, I asked the English gentleman who
worked with Bob Pease at National to tell me what that Rule was -- and bang,
he said it right out, without any hints.