If you get different behavior from sym.tpe_* and sym.typeConstructor on a monomorphic type, it's a bug. (You should never call .tpe, but it forwards to tpe_*.) So if this is not a no-op I would like to see the test where the difference is on display.

If sym isn't monormophic, then calling typeConstructor is only exchanging one bug for another. If you really want to call typeConstructor, preface it with
```
(assert sym.typeParams.isEmpty, sym)
```