Wow. that got weirdly personal. Without going that route, I'll simply say, we are obviously not speaking the same language here. 
"Honestly, the public domain today is what copyright was supposed to be, really."
In the simplest of terms. "Public Domain today" is NOT what "copyright was supposed to be, really"
The are not comparable entities as you suggest, but representative of an "on/off" state.
It's either in Public Doman for everyone to freely ues, or it is copyright and not accessible to anyone but the author/owner/heirs.
Copyright is an "on" state, Public Domain is an "off" state if we are talking binary.
These separate states exist in a continuum of measured time.
Copyright is the period of time where the author/owner/heirs has exclusive rights to the material.
We'll use Sherlock Holmes as an example. Created in 1886. Doyle died in 1930. Canadian copyright expires fifty years after the author's death. Study in the Scarlet was protected by Copyright from 1886 to 1980 in Canada. (in the US it's 75 years as of the 76' copyright extension act, which put Study in Scarlet into the public domain there in 2005).
Public Domain describes the period of time where the material can be published and used by anyone freely.
Thus Study in Scarlet has been in Public Domain since 1980 to the present in Canada (2005 to the present in the US).
"work for hire" was only established in 1976 as a copyright concept. Which is why it's notoriously difficult to defend the numerous claimants against Marvel and DC in recent years as creators sought to reclaim copyrights on Golden and Silver Age characters. Most of them went to hush-hush cash settlement. (i.e. the case of Joe Simon, and the Jack Kirby's estate in recent years).
and YES, Corporations were given the same rights as people in more recent years... which results in the amendments of "lifetimes" to the addition of set number of years from point of creation, given that Corporations are potentially immortal. These corporate entities notoriously have been extending copyrights to keep Mickey Mouse and Superman out of the public domain (keeping the switch set to "on" long after it was meant to). Sonny Bono was the eponymous culprit in that particular act.
Ironically it was these same copyrights extensions that kept Superman in the hands of DC for example, which allowed his original creators' heirs to stake their claim. Their original contracts with DC comics did not extend past the concept of copyright of the period of time when they signed their original deals. Thus, if the Public Domain does not get to claim Superman for public use, Seigel & Shuster, or in this case their heirs, have the right to reclaim their original copyrights, OVER DC's claim to the character. We're not privy to the details of private settlement, but hopefully the Seigel and Shuster families are FINALLY well compensated, even if Joe and Jerry themselves are not alive to reap the benefits.