I think the major problem with matchmaking is bungo not giving any specifics and just saying X > Y now, or more so than it was before
which could mean something or absolutely nothing. only thing you have to go off of is anecdotal evidence. could definitely have a placebo effect
It's definitely an issue, but some of the changes (or lack thereof) are immediately apparent, especially at the ends of the bell curve. WYL was playing in a full party with another streamer and could readily conclude that IB was largely SBMM within an hour. Really, really good parties will see 2 KD players everywhere, and it doesn't take many games of that to know that the player pool is being segmented. In addition, when you see lag in those very games, it's easy to conclude that connection, while it is a factor, is being trumped in favor of skill.
The anecdotal evidence gets pretty spotty in the middle of the bell curve because the pool of similarly skilled players is larger, and more importantly, the performance of those players will be similar irrespective of the weight given to skill or connection.