Even that complaint is lessened lately, since they shortened the tier spread. The only problem with play entire one-tier spread games, though, is that there are hardly ever enough of those tanks in the queue. Seriously, look at the numbers sometime, and I dare challenge you to find an instance of 30+ tanks of the same tier in queue, in any tier. Then, I invite you to declare where arty land on the tier spread, because a Tier 8 arty in a Tier 8 match is a war crime. And then, I invite you to decide where scouts should get shoved in, especially in higher tier (9 and 10) games because there aren't any light tanks higher than 8, and even then it's not really a scout.
Matchmaking exists the way it exists because it actually works. Switching it to a more "balanced" or "effective" system would not work.