They added the ability to drop between tiers because in S3(IIRC?) you couldn't, and some players would hit Gold (Plat, etc.) and then goof around and troll for the rest of the season because they couldn't demote. So there has to be something to keep players honest. But it is really, really, really hard to get demoted between tiers if you're putting in even a slight amount of effort. (Also: boosting. It's much more attractive if you can't get demoted.)
If your progress gets "ripped to shreds... in a fraction of the time" then your MMR is way too low for the division you're in. Yes, if you're in a "V" division and you lose a lot, your LP gains get out of whack. But the alternative is that they demote you down to the next tier much faster.