Restoring that requirement across the board would have a profound negative impact on the biotech (and likely I would guess, advanced materials) sectors. Think of, for example, discovering a useful small molecule, and wishing to build a moat around it while you do the med chem work for a lead compound.
What you describe is the current practice. What I am trying to suggest is that it is reasonable to be able to use a Markush claim for obvious related compounds.
Maybe, but it's not very tractable to have thousands of prototypes being delivered to the USPTO each day. The point of the patent is to provide all the information required to completely recreate the invention and explain how it works.