I've crossposted this around to various YAWR threads with the hopes of getting a dev to comment on it. I even bumped into Chieftan in-game and asked him on the Soviet heavies forum but apparently he wasn't really sure, so I suppose I'll crosspost it again...
I have a game design question as far as moving heavy tank IS-4
to Tier X as an alternative line to heavy tank IS-7
From a design perspective this really doesn't make a whole lot of sense. As it is, IS-4 is an excellent heavy tank - it has a very solid armor scheme that, with angling, can really be difficult to destroy, and with 130mm gun S-70 it can severely maul most enemy tanks just fine.
However, other than the fact that its rear armor is much heavier, IS-7 is basically a more potent and sophisticated design in every way. The sloping on the bow of the hull as well as the turret is especially noticeable - its paper figures are often thinner, but with the richochet physics IS-7 can be very hard to penetrate, even from the sides - especially if its hull is partially concealed.
Historically, IS-4 was a competing design to IS-3. Both were armed with 122mm D-25T - IS-3 made use of a totally new hull with a pike-shaped bow and flat, pancake-like turret, while IS-4 more or less followed IS-2's layout with an angular bow that included a driver's hatch and a turret that was round on the top and bottom (including the irritating shot traps on the edges). IS-3 was unquestionably the more advanced design - it was lower, faster, had a stabler hull layout, and the low heavily rounded turret was basically a testament to Soviet tank design from that point on. IS-4, meanwhile, was essentially just a super heavily reinforced IS-2 with drastically better armor but little else in the way of innovative design features. Compared to IS-7, which had a number of seriously "gee whiz" facilities and equipment to it, IS-4 looks downright primitive even though their development is separated by only a few years.
Now, from a gameplay standpoint, I can see how IS-4 gets bumped over to the "KV" series of heavy tanks. The thing handles a lot like a KV does - it has poor mobility but great armor protection and usually has a big gun. That particular aspect makes perfect sense. What I question, though, is why it belongs on a Tier X platform in the first place.
Historically IS-4 never received the 130mm gun S-70 - that was the IS-7's claim, and the two loaders in that bulbous turret help testify to the necessities of arming such a big piece of artillery. It was tested with 100mm S-34 and 122mm S-34-2, just like the prototype ST-I (which will lead to IS-4 in the new tank line...) but that was all.
So, why move IS-4 to Tier X?
It has exceptionally good armor, but IS-7 is arguably better thanks to the shape and sloping of its hull and turret. It's faster than German heavy tanks, but still significantly slower than IS-7 (especially climbing hills - an E-75 can *almost* keep up on a slope). It has a really big gun, but IS-7 gets that as well, and that particular piece really doesn't make much sense outside of gameplay reasons to keep the tank competitive at its tier.
If you remove the 130mm S-70 from the equation, IS-4 is basically just a much better armored IS-2 with inferior handling - basically what it was in reality.
I'm really just curious if there's a reason for this outside of gameplay purposes. I suppose that's fine, though, since it is a game. After all, on the German tank destroyer line the Ferdinand (early 1943) is a higher tier vehicle than the Jagdpanther (mid-1944), and if you compare their combat ability there's not much to argue with with that order.
EDIT (some personal consideration):
It seems that the issue comes from the fact that IS-4 was probably "over built" for Tier 9 in the first place. The reinforced bow (with the "plug" over the driver's hatch) and the inclusion of 130mm S-70 gun, combined with the already excellent armor protection, really made it too much tank for tier 9. But, with the exception of kowtowing to those who've raged about the IS-4's bounciness (something I really have trouble imagining the people who make this game to do...), all I can really conclude is that it's easier to bump the IS-4 up a tier than to nerf it and bounce it *down* where it really ought to belong. Giving the size of the IS-4's turret, I have some difficulty envisioning the crew actually being able to schlep the 130mm shells into S-70's huge breach assembly in the first place... isn't that why IS-7 has two loaders and such a long turret? The Panther got nerfed and kicked down to Tier 7 when the E-series was added to the German tank tree, after all... surely it wouldn't be outside the realm of possibility to do something similar to IS-4?