You should only be demoted if your loss would have taken you below 75 LP
Otherwise, you just lose more LP than you should have.
I know it balances out because sometimes you get an 8th place that you would have lost 75 LP for but only ended up losing 25 due to the way demotion works, but in general, players (and all sorts of humans) tend to remember negative things more than positive things. Think about it this way, if you went to a restaurant 10 times, and 9 times you get good service and good food, but on the 10th visit, you get a really grumpy waiter and the food tastes rotten, you're probably going to remember that 10th visit much more than the 9 good ones.
It doesn't affect the MMR, so games are not ruined just by making it harder to demote. Ranks in TFT and League are basically just the shiny plaster on the surface anyways, it's always been the MMR that affects who you play with/against.
You should also not be able to demote from an IV tier, and in exchange, each season should come with a hard reset of MMR and LP. Since Riot mentioned they wanted seasons to be about 3 months, I think this is viable without ranks getting too inflated.
Eligiblity for ranked rewards of a certain rank should be triggered when you enter the rank, so even if you drop out of Challenger, you should have a reward for even reaching Challenger in the first place. After all, someone who reached Challenger near the end of the season is just as challenger as someone who reached Challeenger in the middle of the season. There's no reason why the former gets ranked Challenger rewards while the latter doesn't.
Overall, this would reward players for playing more (as with these changes, players are expected to climb slowly over a large sample of games) and players would be encouraged to play ranked on their main accounts instead of creating smurf accounts that ruin low elo players experience. Right now, there's a big problem with diamond+ players saying they only play the minimum amount of games to not decay while mainly playing on smurf accounts.
