Are you asking why Ranked Fortitude isn't visible? I believe it is? I'm not sure how it's a gacha mechanic. There's nothing random in how your Ranked Fortitude increases are calculated. It's based on merit.
Or are you asking why MMR isn't visible? I could foresee it being visible at some point --- it's commonly visible in some form in other games. The new icon we are adding is an indirect way of showing MMR (if you see the icon, you know that players' MMR is closer to the rest of the players than their rank would indicate).
When you are getting about the same LP for a win as a loss, that's also a signal that your LP = your MMR, if that's helpful. It's not hidden for any nefarious reasons, but I think more because historically it's tricky to represent in a way that isn't confusing. MMR can move a ton more or a lot less than you might expect because of the math involved.
MMR's goal is different than Rank. MMR is meant to precisely predict the outcome of a match and be the best guess of how you will play in the future. To that end it should be free to bounce around as much as necessary to be accurate. Rank, on the other hand, is to show what you have actually proven and earned. It's more about your past than your predicted future.
I've worked with skill systems that can predict a player will be a Challenger after only 1 match in many cases. But it wouldn't be fair to just give that player Challenger without them proving we were right (or not if we were wrong).
On the topic of matchmaking teammates vs. grouping teammates, that's definitely something we can revisit as we roll the changes out. I'm not opposed to reconsidering it upon observing the data.