This is my opinion built of observation and learning about MMR. I have a Base assumption that riots Titles are designed to represent a static MMR range for low uncertainty accounts. Similar to the way many other companys and orginsiations desige their titles. Chess being one that influcanced my oppenion here strongly.
A follow up assumption i have made is that your LP gains are in relation to the gap between your assigned MMR and assigned Title to move your title into the direction your MMR is located. This is just elaborating on what is a commonly accepted assumption for how Riots system works.
You can instead see systems where Population can be used via a percentile system but as player population is so volatile that imo makes for a terrible metric if you wanted your Titles to represent skill in relation to your MM. It also does not overlap or interact with Elo systems as well as a static Title system does. Chess, for example has Titles like Grandmaster for players over X Elo points.
Because MMR is W/L in relation to who your playing, if you up your WR at your current MMR to be a more dramatically high # you will add a gap between your MMR and Title to the point it will bump up your LP gains. Unless it gets to a point where K factor has been lowered so much that your Lp gains and MMR gains are identical values. Then your unable to build a MMR to Title gap unless you fail lots of promos via dodging or other behaviors to artificially gap your MMR and LP.
MMR and Elo systems ever lock you down, at no point does it say This is forever your rating. Its meant to be a range, its meant to adapt to new information, its for all intents a self correcting system.
That they can be grindy is really the worst thing you can say about it.
