Better simplfiication for big types

The generic machinery is sadly not getting simplified away for big enough types. For an example, see the test case `eqBigR =/= eqBigG` in `test/inspection.hs`. The generically derived `(==)` (`eqBigG`) simplifies to a `join` point applied to a `Rep` in each of the 5 branches after pattern-matching on the first argument. How to get this join point to be inlined?