There's so much more that humanity needs to understand about sexuality before developing these drugs. Clearly libido is different from engorgement.
Guys using Viagra-type drugs often report that the drugs don't furnish any libido, and "a boner is no use if you can't feel anything." Obviously, these are guys who have been using too much internet porn. But that may be a huge percentage of the ED population today.
As long as we measure success in markers like episodes and erections alone...we miss the forest for the trees. And, of course, no one is thoroughly studying the after effects of orgasm on either sex.