I was think over this for a day or so, and the fact that you are waving it off makes so sense. Here's why.
1. (most important) If you can use heavy weapons good enough to counter something like Truth, SSimulant, or Qullim's Terminus, why be in a compatible match?
2. Heavy is like a super, it is used only every now and then and is meant to give a few easy kills. Then if you are very good, you can make sure you don't get killed by heavy. Don't get me wrong, I know I have casual-like stats, but I am reasoning with logic here.
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Your second reason is flawed for the fact that one team will have heavy and the other won't depending on who kills who when it drops. Then you're left with one team having a massive advantage over the other, especially if they have machine guns. Its the biggest crutch and requires absolutely no skill to abuse. Heavy should only be a thing in 6v6