I was never a fan of dividing bronze into iron and bronze and adding a grandmaster tier. It's redundant when matchmaking still pairs you up with people significantly below and above your current rank in order to shorten queue time. Currently having more ranks is nothing but a superficial way of putting a new paint job on a shitty infrastructure. Dividing ranks would only be useful if you are only made to play with people inside said rank.
The current system matches people by mmr, but the same mmr can appear as different ranks, which is why a plat 2 player can still have a diamond 4 and a gold 1 player in their games. Now assume the Gold 1 has a MMR of Plat 4 and the Diamond has a MMR of Plat 1, and everyone else has their correct MMR for their rank. A team such as:
TEAM 1: Diamond 4, Plat 3, Plat 3, Plat 3, Plat 2
TEAM 2: Plat 2, Plat 2, Plat 2, Gold 1, Plat 2
could potentially be made with the team MMR on both side being close to identical, but the Max-Mix difference in each side would be huge. The Diamond 4 can easily exploit the Gold 1 player causing a huge favor to them despite both team having "similar" mmr.
The only way to fix this is to accept the increase in queue time and having everybody play against people in their same rank while still using the current MMR system to form teams. That way, the diamond 4 player would only be matched with other diamond 4 players within their MMR and the gold 1 only against people in gold close to their MMR.