Stat squish confirmed: How will unsynced old content be handled?

[Seraphor]

It surprises me that we have to do these things with even such small numbers, it is not that we reach the million damage currently to do this and in the end it makes it clear that the game code is garbage.

You have multiple people dealing damage on a per second basis. So those 5000 dmg hits add up quickly to ridiculous numbers when you need a fight to last 10+ minutes.
This is why enemies have HP as high at 440 million.
It's simply not practical to code for values much higher than that when you need to relay them over an online connection, along with all the other data that get's sent back and forth as you're playing the game, in real time. It could cause issues that exacerbate people's lag with low ping, fail to apply damage within a certain window, etc.
It's something all MMO's deal with. WoW just had their own stat squish, and took everyone back down to level 50.