This is wrong.
First off, with bonus stars from a higher finish a previous month, you get double or triple stars and barely need any winrate at all.
Second, even if you have zero bonus stars, there is a win streak bonus for Diamond 6 and below, where you get 2 stars per win if you win three or more in a row. Because of this you will maintain your rank long term (even without a rank floor) if your winrate averages 45.34%. Therefore it is possible to climb out of what I call the participation trophy ranks with sufficient time even with a winrate of 46-49%.
Technically yes, but this has even less of an impact than win streak bonus stars at D6 and below. I actually previously did the math here: "Brute forcing" to Legend
The TL;DR is that unless you’re a bot then you don’t have enough hours in a month to pull this off with a winrate below 46%, unless you get very lucky. And even then 46-48% winrate will require an absurdly tedious level of time commitment, again on average because luck is a factor. It’s just so much cleaner and faster to actually be above 50% winrate.