I quite agree with what you say, Klyde.
I think the reason for that is that there are not enough people queueing, and after some time, the matchmaking algo matches 2 teams eventhough their rating difference is huge (the logic is that it is better to have matches more often even if the rating difference is big instead of rare matches).
I think this problem can be solved if more people play arena, and if all the friction around finding teammates and queue is removed. One idea I had for that is this: Solo queue in ranked Arenas
More people => More likely to find people around you rating