Title says it all.
When promotional games were added to usher in the start of Season 3. I naively believed that they would be helpful for keeping players in the rank they belong.
While this is technically true, and they have succeeded in that respect. They have come at a devastating cost.
Tell me, when faced with the likelihood that there will not be a single Diamond+Crystal game played all season how would you best attempt to become Crystal ranked yourself?
After all, this was almost the reality for many players on Materia in Season 3.
The Answer: Intentionally lose games.
For those of you who don't know, or don't understand why I would claim that the best way to rank up involves losing: When you reach 3 stars at the top riser in your tier, (eg. Diamond 1, 3 stars) The matchmaker treats you as if you were already a member of the rank you may be about to enter (in this case, Crystal). This changes the players that you can be put into a match with. Because you are treated as being in Crystal, you can only be placed into games with other players that are Diamond 3 or higher. (In the case of Materia in season 3 this leaves your potential match pool with at best 59 players. This number both includes alts (that's another discussion entirely), and that it seemed like people in D5 were being dragged into Crystal games.)
Because of this, people who became D1 3 stars were considered to be "in purgatory". As they were both not Crystal, nor able to get matches to advance or leave.
Knowing this, how does one avoid purgatory? How do you enter Crystal without ever playing a Crystal game?
Simply skip your promotional game by exploiting the win streak bonus.
And if your potential win streak bonus isn't going to line up?
That's right, time to throw.
Throw and lose until you reach diamond 2 with 1 star and pray you win the next 4 games in a row. And if you lose your 4th match? Better get back to throwing.
I only realized in writing this that you can't start even your climb at D2 3 stars because if you lose at D1 0 stars you go to D2 2 stars instead.
Ideally ranked wouldn't have these hard cut offs and I would have been able to get even a single game on the first day of Season 4. But because it does; I didn't, and losing can be beneficial. A better solution would require overhauling the way ranking works. But eliminating an incentive for people to grief only requires them to change back to the way things were in Seasons 1 and 2.
TL;DR: Promotional Games and the current state of matchmaking in general provides players with a mechanical incentive to throw games. Something needs to change.
Edit: It feels necessary to tell you NOT to do what I'm describing above as doing so would be in clear violation of the Terms of Service. The instruction is purely there as a demonstration of how flawed and rife for abuse the system is. I want to enjoy ranked without the fear of somebody throwing their game because they can't reach Crystal otherwise.