Ladder ranking (LR) is (presumably) like hidden Matchmaking Rating (MMR), but offset by an unknown amount, and inflated by Bonus Pool.
Ladder ranking changes similarly to MMR, rising and dropping depending on the relative strength of your opponents, but it becomes offset by following factors:
- LR has different "zero point" in different leagues (and League ranges should not overlap much, theoretically).
- LR cannot be negative, so if you keep losing, your MMR diverges from ladder points.
- LR is inflated by Bonus Pool, so, assuming all players spend their bonus pool, everyone's Ladder points drift up from their MMR by some (same for everyone) amount.
There was also a nuance that when matching players, their relative strength was determined by subtracting MMR of one from LR of the other, so both players could turn out to be "favored". "Favor" indication was removed, though, so it may have no effect today.
Bottom line: while LR does correlate with MMR in some circumstances, strictly speaking, it does not mean anything but rank in a Division. It is (with all Bonus pool stuff) just a convenient way to rank players, while giving them sense of progression and "catching up".