Speaking of the level of competition, and how different the game is today vs. the past when QB's weren't so protected, I would like to offer up a possible counterpoint:
The defensive players of today are way, way, way more athletic than the defensive players of 30-40 years ago. The linebackers are so much bigger and faster, as are the d-lineman. They are literally freaks of human nature.
If you took a time machine back to the 70's and 80's, and even early 90's, and told them that in today's NFL you have defensive lineman and linebackers who are just as big or bigger running 4.4 40's, they would tell you that you are either insane or everyone is on dope. Meanwhile, the OL have gotten bigger and more athletic, but not near to the same level as their defensive counterparts.
So yes, today's QB and offense as a whole is way more protected than in the past, but the defenses today seem way more athletic, faster, and stronger.