I'm clearly anti-Glennon. I just don't believe he has the potential to be a very good to elite quarterback in this league. I believe you need a difference maker at the position and I don't think he is one.
That being said a lot of Glennon supporters seem to think that the best route is to build up the rest of the team. That the offensive line is most important or that you need to build up great units before getting a quarterback. But you can't do that in this NFL. There is a salary cap which forces you to cut some players and only keep certain key players. You can't have it all.
Quarterbacks in today's NFL tend to carry the highest salary cap. This especially makes it difficult to keep so many great players. As you just don't have the money to pay everyone. With the salary cap you see a lot of teams build successful teams by having a franchise level quarterback and having key players in various other spots on the team and then being able to put almost anyone in the remaining spots (not really anyone, but not the most elite players/greatest players at each position either).
This means you can't have complete units, but you can have a few key players that carry high CAP numbers, one being a franchise QB.
So look at this in the future assuming we keep Glennon. Say we draft great offensive lineman, and wide receivers to put around Glennon (also assuming they were great draft picks that all pan out). In 3 to 5 years when it comes time to give extensions, you look at Glennon and on the surface it seems he has played well (This because of the great "units" around him). So he would get an extension as he would probably be seen as the Franchise guy. Well now, what about the other players? Glennon being a QB is going to carry a huge CAP number. Meaning not everyone on those great "units" will be able to stay with the team because there isn't unlimited CAP room. So what happens? They don't get resigned and we look for cheaper talent elsewhere to take up those spots. These "units" become weaker. But if these "units" were the things that made Glennon play well, what is going to happen when they aren't complete or great "units" anymore?
Teams like the 49ers and Seahawks have a lot of talent since their quarterbacks are on their rookie contracts. But when it comes time to give those players franchise QB level contracts, the talent around those players will go down. Building the team around a QB on his rookie contract number limits you to around a 4 year window of success. But with a quarterback that can be very good/elite, one that can overcome this talent loss, your window of success is extended for many more years.
This is reality of the NFL. You can't have elite players at every position. You have to have a great QB that you feel confident in. One that you feel is worth this high CAP number when it comes time to make money decisions on other players. One that is worth having to cut other talented players because of the lack of CAP room. One that you feel confident in being able to overcome the lack of elite talent at other positions.
I think this will especially be seen now with Andy Dalton coming up soon with needing a new contract. Do the Bengals view him as a guy worth this huge CAP number? Do they think he is worth giving up some elite talent in other parts of the team? Do they think he can overcome the loss of talent?