Too much to grok right now.

There is already a convention for what a decorator wraps. It is __wrapped__.

https://github.com/python/cpython/blob/3405792b024e9c6b70c0d2355c55a23ac84e1e67/Lib/functools.py#L70

Don't use __func__ as that has other defined meaning in Python related to bound methods and possibly other things as well and overloading on that will break other stuff.

In part I suspect a lot of the problems here are because things like classmethod and functools style decorators are not proper transparent object proxies, which is the point of what the wrapt package was trying to solve so that accessing stuff on the wrapper behaves as much as possible as if it was done on what was wrapped, including things like isinstance checks.