That's just the general idea. Don't take that for granted. For example, British tier V light tank - Crusader - has great DPS potential, with its very fast firing gun, making it perfect for wrecking shit from behind or flanks, coupled with its good mobility.
A better description would be one of the different nations.
Brits, for example, seem to have mainly tanks with precise, fast firing guns with somewhat lower damage than others (but still a high DPS). Their heavies are slow, but with a ton of hitpoints. Their light/medium tree has generally fast tanks, good for flanking.
Germans heavies/mediums seem to average on pretty much everything - average damage, with average penetration and firerate, average armour, decent precision, average mobility. This makes them rather flexible, but lacking in certain strengths. Their TDs have absolutely great precision and very good penetration, whilst also being heavily armoured from the front.
Russian heavies can be very heavily armoured and with sloped armour too, whilst having super slow, rather inprecise but extremely hard hitting guns. There is a faster, slightly less armoured tree and a slower, more heavily armoured path for these tanks. Their mediums have good mobility, decent guns but poor armour. Their TDs tend to have the hardest hitting guns of all TDs.
American mediums have good mobility, decent armour and fast, but not hard hitting guns (though slower than british guns). There is also a new tree with mediums that have autoloader guns - these do extreme burst damage, but have a long reload time between bursts (i so want these). Their heavies differ from tier to tier - tier5 and 6 heavies are mobile, with relatively fast guns, great for pushing an assault. Tier7 and above heavies are rather slow, large, but very heavily armoured (especially the turrets) and with a powerful gun. Their TDs have two branches - one with less heavily armoured TDs, that have turrets, and a more heavily armoured turretless (at least above tier6) TD branch. Guns are relatively average and the same in both branches.
Can't tell much about chinese or french trees. Chinese seem to have a very similar heavy tank line to russians, with perhaps different guns and an interesting light tank line, but i'm yet to get above tier4 in their tree. Gotten just as far with the french - they seem to have totally great light tanks, when you want to scout, whilst dealing some damage as well. Their heavies have autoloader guns at higher tiers (meaning high burst damage) but seem to be poorly armored - basically glass cannons.
Oh, and another thing - the actual division between light, medium and heavy tanks only really starts at Tier 5. Anything below that is just tanks - somewhere between light and medium. Tier5 is where the tanks-proper begin.
