There are a few ideas to keep in mind:
#1: The slot safety to both sides of the field generally work as alley players primarily, meaning the assumption that they are reading the same things you think they read, aren't likely to be true. Their primary read is the last man on the LOS looking for a run/pass read. If you are apt to pay attention to RH/GR/ and other safety footwork, you'll notice they step down hill into the slot or sideway (looks like a shuffle step).
#2: The pass read isn't straight up look at the slot. Generally speaking they look for a vertical release (eyes on #2) but if they have an in break or out break they then work outside in. In most mixed coverage concepts, whether it is a 4-2 or 3-3, whether RH's side is playing man or zone, the read should be through number 2 to #1 (the most OS receiver).
#3: The alley player either starts at 12 and creeps down hill, even on a vertical release, or shuffle sideways at 10 -12 yards. This compresses the recovery space, and in most cases they aren't taught to play over the top of the seam but rather conflict and trail. Leads to some big plays time to time, but generally this philosophy is pretty effective at forcing the QB to put air under the ball that helps with recovery time.
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From a coaching perspective, defending the slot release is pretty difficult. In the spread era, most defensive guys have stopped trying to get a hand on #2 because it stretches you so much in run support. If you put your hand on #2 because of how far out a lot of the 2x2 and 3x1 put #2, you either stretch your OLB or SS so far out they are turning their back to run support. So the goal for a lot of teams who have committed to 5 or 6 DB's is to go 3 over 2 eligible receivers (1 CB, 1 safety and a edge player). That doesn't always happen, but your goal is to prevent the the quick seam by putting a guy (typically someone like Hauck) in the QB's vision so he doesn't fire that quickly. You are giving up some soft slant coverage but the overall goal is to rep the down hill alley track so that receivers are less likely going to want to come across the middle on the shallow under routes against the safeties.
Plus one thing to remember, is that for the totality of snaps over the course of the year, teams didn't exactly brutalize the middle of the field. This is a bit of lets fit a low percentage of plays (lets say 5% of total snaps all year) into a larger narrative about a player and a defense. It is one thing to say Robby is slow and can't cover a slot guy who runs a 4.4 in a vertical foot race, because the reality is there are four guys at the FCS that can be tasked to do that.
Moreover, the number of times I have heard 'botched' coverage from a TV analyst over the past 10 years when they are talking about a seam release where merely they were beat in man coverage, I'd be a rich man. Too many of them still think they are looking at some sort of shell coverage, and its just man. That's it. When you send pressure and the offense is able to heave (Barrierre style) a floated vertical seam route, you tip your cap and move on. Its not failure, in most cases and much of the defensive staff will second this, the offense merely executed. It is one thing if teams are completing 3-5 of these routes a game for big plays, but they aren't. Most of the season we might have 1 or 2 plays.
I get that some don't like it, or just don't like Robby, but they aren't going to sub Robbie out on third downs. He's not a liability in the way that many think he is, but rather he is doing exactly what is asked of him on a great many snaps. Your issue is with the scheme then and not Hauck. To that the criticism is fair, but for the staff and a lot of 3-3-5 guys the benefits of the system far outweigh the risks.