Tried to use flex queue as replacement to ranked 5's, was unsuccessful

I am a casual League player who mostly just plays with 4 real life friends. In the past, me and my friends have always found joy in playing as a 5 man ranked team. After going through most of last season without ranked 5's we were ecstatic when they brought it back, even with the specific time constraints. Our skill level is varied enough that dynamic queue was never an option due to the gap in our ranks. We did play normals when it was all we had, however, we get more enjoyment out of the game when we are playing ranked 5's together simply because it gives us something to strive for. As a result, I have noticed we play this game much more often, when ranked 5's is available to us.

So this season, we were bummed out when we found out that ranked 5's was again getting the boot. Upon learning more about flex queue and how it would have a separate mmr from solo/duo queue we thought we might be able to use flex queue as our ranked 5's queue as long as we only played flex queue when we had all members of our team present. We did this and just finished our placement matches last night...and were all received a different rank, from Bronze III to Gold V, despite playing all of our flex queue matches together. This means that we can no longer play flex queue together.

So, I guess the point of this post is to explain that flex queue is not an adequate replacement for ranked 5's. I understand this may be a unique situation and perhaps there aren't many others who are experiencing the same frustrations, but I wanted to voice my experience.