I generally agree with your post but I think you are wrong about the 2014 QB class in that I'd rate only 1 of the 5 QBs you named as a "hit". Only Carr has developed into a decent starter. That's not saying he's a franchise QB yet but he's probably worth more than the 2nd round pick the Raiders spent to get him, something that can't be said all that often about QBs taken in the first two rounds of the draft -- or the other QBs in his draft class.
Bortles regressed badly last season, something that's an ominous sign. It suggests that he hit his peak back as a sophomore and isn't going to improve significantly, so he's probably done. The only QB since the merger who started out well, regressed, and then continued on to have a stellar career was Drew Brees. Count Bortles as a miss IMO.
Bridgewater is probably finished because of his injury, but even before that, his game had serious deficiencies, particularly his apparent unwillingess to go long. Maybe he would have overcome that as Tannehill seems to have done, but it's likely we'll never know. I hate to count him as a miss but he's a question mark at best.
Garoppolo hasn't proved squat yet. He started 4 or 5 games in his NFL career. If he was that good, Brady would have had a harder time getting his job back or maybe not even gotten it back at all. Remember, it was Brady who took over for starter/Pro Bowler Drew Bledsoe in 2001 and never looked back. The chances are that Garoppolo is closer to Brock Osweiler than to Tom Brady. Another question mark but likely a miss.
Manziel shouldn't have been drafted in the first round at all ... and probably not until the third round at best if not the third day of the draft. The red flags on him were well known. A big miss.
Generally speaking, over the years, drafts have yielded about 1 decent starting QB. Occasionally, 2 decent starters will emerge (2008) and sometimes all of them will be duds (2007 and 2013). Usually there will be 1 or 2 decent backups/low quallity starters who come out of the later rounds, although often first rounders will stick around as mediocre starters and then backups for a while. This seems to hold true whether there's 1 or 2 QBs taken in the first round or 4.
The best QB draft EVER was 1983: Elway, Kelly, and Marino were all HOFers and Ken O'Brien was a decent starter for several years. Still, KC took Todd Blackledge before Kelly and NE took Tony Eason before Marino. The next best class was 2004 when Eli Manning, Rivers, and Roethlisberger -- all likely HOFers or considered for HOF -- were taken in the first round. Of course, so was JP Losman. Matt Schaub, taken in the 4th round, started out as a useful backup and had a couple of years as a decent starter.
2012 seems to have been the best QB class since 2004. It's yielded one definitely special QB in Russell Wilson, who was not even taken in the first round. Andrew Luck has definitely been successful, although it seems that he's been a bit of a disappointment recently as he's not improved his game as much as one would hope. He was expected to quickly progress to the level of Brees, Brady, and Roethlisberger, but he doesn't seem to have made the strides he needs to reach that level; he still makes a lot of mistakes that he made as a rookie/sophomore. Is it coaching, maybe? Still, most teams would welcome him to their roster if they got the chance. Ryan Tannehill has also become at least a decent starter, perhaps even more, after a rocky start, and Kirk Cousins has come out of nowhere (the 4th round actually) to be another decent starter.
It really doesn't matter how these kids are rated by draft gurus or even by organizations. It matters how they adapt and play the pro game, so if 5 QBs are rated higher in 2018 than any of the guys taken in 2017's first round, it means squat unless they turn out to be successful NFL QBs.
