For heavies you oftentimes just need to play more conservatively. KV-3 may seem completely outclassed by the IS but they have the same alpha and similar armor (in fact the IS can sometimes be more squishy.) KV has outrageous alpha and penetration for its tier. The PZ4 has enough firepower and a playstyle that allows it to cripple its higher tier mediums at long range. The E8 can out maneuver a T20 and in cases of extreme player skill beat it through sheer DPM and agility (usually impossible with any other medium vs higher tier med.) The T-34-85 has a powerful mantlet that typically bounces 175 pen. If you find a tank corpse to hull down on you can take on stupid KV-13, T-43, KV-3, and IS drivers (smart ones will just rape you in brawl.)
T-34 has very high DPM for its tier and given similar exposure as an ally your enemies tend to shoot your ally first. This often gives T-34 drivers outrageous flanking opportunities where it can use its DPM until your enemies fatally realize how deadly you actually are.
It's true that the MM is never "fair" for lower tier tanks. It just provides you a better opportunity to hone your skills in much a much more important skillset.
I often play mid tiers and am very used to not being up top. It's simply a matter of lowering your expectations for the match. You can wade into a brawl as a KV-3 like you would as the top tier. Instead, you can play with this in mind. Oftentimes if you expose yourself at about the same amount as your higher tier ally your enemies will shoot your ally instead of you. This effect increases with range, as your enemies need to turn their gun AND aim. Usually they won't change at all because they're vulnerable to the bigger threat while they re-aim their gun. Learn to use this to your advantage but realize that when your ally stays behind cover for too long (or is exposed in a way that's difficult to hit,) he's no longer a tempting target That's your cue to retreat or stop exposing yourself. In the meantime you can get free shots in, relocate, move to a flank, and in general have a lot of opportunities to affect the match. This obviously never works on a 1 vs 1 and is one of the skillsets for a good opportunistic type player.
There are other skills that are irrelevant to one on one fights but are oftentimes more valuable for the team. Knowing when you're free to move despite being in the enemy's line of sight definitely tops that list.
Edit: I specialize in this so much that oftentimes I suck like hell in 1 vs 1 fights. I hate it when I'm top tier of the match
you are definitely correct that in a 1on1 you won't be able to the skill set such as flanking when the oppertunitely arrives.
but say you are stock or atleast you have gotten some but not the most important module of all (the good gun)and you try to flank someone 3 tiers higher, no skill in the world is gonna help you penetrate. i've had moments where you ganged up on the enemy and because i don't have enough penetration, shooting them in the back meant ricochet. i don't have great stats, so you can easily say that one crappy players who are putting down stats because he has a bad stat. but i know the fundamentals of this game, i've played red orchestra ostfront. i know about tank angling/ weak spots, sloped armor etc well before i started this game 3weeks ago. all those only give me soo much of a chance, when your don't have all the fancy upgrades, and the decent crew percent, and your basically up against a tank your no match for, theres no chance. when i aim in this game, there are two things i look at, is the reticle green, and is it flat area (least angled spot). and most of the time, when i fire, it ricochets if the tank is tier 2+ higher.