The groups' speed up the tower. (Spoiler)

1. People seem to be quite wrong when they think that Urek becoming ranker in 50 years is only impossible. Urek broke the record for 50 years, but it doesn’t mean he is very very far from the 2nd place. U can compare to Usain Bolt running, he breaks the record for finishing in 10 second, but it doesn’t mean the 2nd cannot finish within 12 seconds or so. People tend to think of how a monster Urek is, and exaggerate the time that he used to climb the tower. I expect an elites of elites team like Baam and Androssi can climb the tower in less than 100 years.
2. You don’t need to be a monster like Urek or Baam to speed climb the tower. Most of the tests tend to be pitching Regulars against each other to compete. So you only need to be very strong team to not lose to other teams, be lucky to not face monster teams like FUG, Jahad princess and so on, and be not goofing around. Then you can speed run the tower just like the Jahad princess.
3. Koon hasn’t caught up to Maria, you are wrong. The twin princesses, as Isu mentioned before, they should be staying at 40-50s floor right now (Im sorry I cant remember the number). It means they already climbed 10 floors above the team or so. They are only goofing around here, and that, as I told, also contributed to they being slowed down.

The thing about Urek is that he's already way strong before he came to the Tower. God of Guardian specifically mentioned this, and being strong does help on many occasions. The group is going pretty fast is because many of them are exceptionally regular (I like to call them super regular just like super rookie on One Piece) e.g Irregular, Two Zahard Princess, three people from the 10 Families, a Living Ignition Weapon, a Guide and a Dinosaurs (feel free to add more), not to mention the support from FUG too. Just like you said, it's quite likely that the higher you go the more difficult the test would be. That's why it takes hundred of years to climb, while not all regular will become a Ranker, many of them gave up climbing or even worse got killed in the process. One other thing, the group took The Hell Express to get from the 35th Floor to the 43rd Floor quickly.

I think you hit the nail on the head with the exponentially harder part. Remember Yeon climbed the first 20 floors in 5 years. Yeon! If you look at it, these teams have been forced to push through FUG, Slayer candidates, and an irregular test. The teams consist of T1: 2 Zahard princesses, 2 very talented scouts, and an adapting team in regards to members. T2: A direct descendant of Koon, monster of E class Nobic, a literal monster created by the workshop, and the fastest scout. T3: Yeon, who like Kaiser has the strength to b a princess but isn't one, strategists Koon, and not a whole lot else, excluding an immortal guy. T3 is the only normalized group. They have a bunch of outcasts who weren't strong enough alone, but together could climb. T1 and T2 are climbing fast because of great teamwork and enormous amount of strength.

All in all, they aren't on a Urek pace, just fast as the next floors will take much longer

Dude, the paid chapters are taboo. Don't talk about them here since most people are unable to read them. Just a heads up, though mods should probably make it more apparent.