I believe LP gains and losses aren't based on your opponents MMR, but your own relative to the mean for your rank. Basically, if everyone had 50% winrates, the system would force people to a rank that corresponds to their MMR. If you're losing more than you gain, it means the system thinks you should have a lower rank than you do, and is trying to force you there.
What you're describing IS part of how the Elo system works, just not with LP. You'll lose a hell of a lot less MMR than you'd gain playing against higher MMR opposition. But your LP losses should be the same if you're losing to the whole TSM roster queued together or a bunch of bronze V's.
If your reaction to this is "wow, the ranked system is a stupid coverup for my Elo and doesn't really matter" then you're starting to get it.