My sense is that most of the open argparse bugs are *because* of the increased power (that is, they aren't, with a few exceptions, in the fundamental bits that optparse does as well).  And the issues are open because no one is maintaining that module, either :(.  There is one non-committer who has done a lot of work on the patches, we should probably evaluate offering him commit privileges.

That said, I don't have a strong opinion on the deprecation-or-not myself.