Just something for each player to consider, as a little test take note of your current rating and mark it down on paper or in a text file or something, do this each day/week and also make notes of when/if you spend and when you go on a losing streak (also during the losing streak check if boosts are for sale, I have another theory about that).
Keep track of this infomation and see if you are actually getting anywhere (as in moving up) or if you are stuck in quicksand and stuck in place.
I say about keeping this stuff written down because you cant go by your feelings day to day, as you will lose some matches and win some, but if you cross reference this with you notes you will see if you are stuck in one spot forever no matter how much you play/grind/spend.
Treading water is very profitable for a company, because it keeps the player exactly where they are, spending the whole time to try and get out!
Now, are you one of them? (might take a few weeks to see for sure).