This is interesting for sure. I would love to see charts like this more often from them. I would also like to see a breakdown of causal play queue and ranked queue, but I assume if they won't include it, they are roughly the same.
The one thing that is surprising to me is that alchemy is twice as popular as explorer. From my experience in ranked BO3 queues, explorer pairs you up with an opponent of similar rank way faster than alchemy. In alchemy queues I have 1+ minutes of waiting time and often getting paired against the same person or people from way below my rank. This happens way less often in explorer. Maybe it's just the timezone and when I play arena that affects it. For the longest time I assumed it has to be the casual play queue influencing the percentages, but them not splitting them up second time around makes me think this is way less likely to be true.
As for brawl it would be interesting to see if they abandon standard brawl completely. Is there anyone who prefers it to historic brawl? Maybe it's more new player friendly?