How does it keep kobolds comparable to dragons though, and why is that a good thing that both would be always just as threatening?
I wouldn't say they are just as threatening.
But the bounded system is such that a kobold is far more likely to do some damage to a high level fighter than in Pathfinder (which I still love). A high level fighter can still wade through many kobolds (multiple attacks, bonus attacks, special abilities, and a lot of HP), and a single fireball will take out a cluster of them.
The how comes down to attacks tend to start at +4 or +5 and ACs rarely get over 20. (They can get well over 20, but not routinely). In PF the kobolds are looking for that 20-always-hits solution. In 5E they are going to hit 25% of the time(ish).
In PF a group of 20 kobolds is just flavor text against a high level party. You can have fun playing it out, no doubt, but it can just be a delay to the next big encounter. In 5E the ability to crush the kobolds is not in doubt, but stopping to just scare them away or avoid them altogether can also be real considerations simply do to the resource use the fight will take.
If you are in a fight in PF with a big dragon and he has a bunch of support (standard) kobolds, they are again mostly background. In 5E if they all bum-rush the wizard, they can be really annoying as they plink away at him.
These things work in PF, but 5E really outshines it here.
My group has been playing PF since it came out. We have now played 5E up to L7. I asked the players for their view and they said that for the most part, it was still "D20" to them, but they recognized the different balance of threats and that was cool.
I think "at the table" I see more differences then the players do.