BUG: agg with axis=1
This is a potentially inefficient fix to the this issue which requires a double transpose. I am unsure how inefficient this is, and if this is an acceptable solution. It solves the issue, but perhaps it would be preferable to implement this further down the stack in `_aggregate_multiple_funcs`.

An additional small fix is to pass `_axis` down the stack. `axis` was passed to `self._aggregate` previous, but had not effect since it was not referenced.

- [X] improves #16679 
- [None] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
