No it is not the main battle tank that is the issue here as that one require uranium and while the medium tank upgrade to it, you need in general atleast 3 more techs, Composite Armor to unlock the main battle tank and two techs Research Institute and Uranium Separation to unlock the uranium mine. The  issue is the other unit unlocked with Composite Armor, The Armored Person Carrier (APC), lets compare medium tank with APC:

Medium Tank on left APC on the right:

• Combat Strength 61 vs 62, so APC is slightly stronger
• Range 6 vs 6, so no advantage to either
• Movement 8 vs 8, again no advantage to either
• Special Ability, non for tank, Suppression for APC which is a powerful ability that give enemy non armored units -5 strength and block them from moving a huge advantage for APC.
• Both are classified as armored, so both are immune to the surpression debuff but vulnerable to armor piercing, no advantage to either.
• Industry cost 7400 vs 3700, so APC only cost half as much, yet another huge advantage.
• Population cost, 2 vs 2, no difference.
• Resource cost 2 iron and 2 oil vs 2 iron and 3 oil, this may be the only reason keeping the medium tank in use as you need one more oil to build APC.
• Technology Continuous Track for tank which is the prerequest for Composite Armor needed to build APC, so the tech gap is very small.

You did not seem to take into account the fact the unit is armored (edit : I'm not sure if the APC has also that stat per say, my apologies if it's not relevant, I was a bit hasty). I mean... it do not make that much difference in battle from what I've seen, but it's still there. (But yeah, even with that, what painfully and masterfully make your point. Tanks are not that great all things considered. Which, in itself, is somewhat realistic by the way.)

Aeram wrote:

You did not seem to take into account the fact the unit is armored. I mean... it do not make that much difference in battle from what I've seen, but it's still there. (But yeah, even with that, what painfully and masterfully make your point. Tanks are not that great all things considered. Which, in itself, is somewhat realistic by the way.)

Both the tank and APC are armored, so no advantage to either. Armored is important as it make them immune against surpression debuff but also make them vulnerable to armor piercing from anti tank gun and main battle tank.

Goodluck wrote:

It was a year ago

It's spam.  If you look closely, there is a very subtle link in the post that you just quoted (which you may want to remove from your quote to protect other users).