The thing however is that often the firepower of a IFV is more useful than the firepower of a tank in most low intensity conflicts and the armament of the standard modern MBT is optimised d largely to engage the one target they don't often meet on the modern battlefield.
Modern conflicts showed usefulness of tanks. Russians used tanks during the second chechen war quite an effectively even during cityfights (it was a matter of tactics which was just plain horrible during the first war). I'm not speaking of the Russo-Georgian comflict in which russian motorised infantry battalion tactical groups of routed georgians with far supperior tank performance (even though 58th Army's tanks were worse than modernised georgian ones). Americans used Abramses quite an effectively, the syrian army don't start an operation against insurgents without the battle-proven T72's. It all was the low intensity conflicts where tanks didn't fight another tanks.
If we talk about MBT armaments, yes, you are mostly right, it is a legacy of Cold war. But still a 125 mm gun is a huge advantage against infantry of any kind. HE-Frag shells with programmed detonation of T-90s are a horrible weapon which negates most of the field fortifications. Even in a cityfight the direct fire of a tank is a must as it can devastate concrete buildings turned into fortresses. For example, it was common in Chechnia to fortify buildings for low-caliber shell protection, that's why most of the time storm groups were given tank assets as a fire support platform.
Modern IFVs are bad for cityfights due to low protection. Armata class IFVs must be better in that, but still big guns are needed in a cityfight
a light wheeled Typhoon class likely with a high velocity 57mm gun
Never heard of what. Typhoon is just a MRAP. I suppose it will be used by police and internal troops mostly, may be for supply convoys in the Army or a light brigade transportation, but still I never saw a Typoon-based IFV project.
while the medium tracked and wheeled Kurganets and boomerang respectively should be able to manage the 125mm gun like the 7 ton lighter Sprut does
It will be self-propelled AT guns, nobody would use it like tanks as the medium planforms are lightly armoured. Throw them into a city or on a spearhead of an advance and they will be burned. Upgraded T72s are now suppoed to be tanks for medium brigades. They will form tank battalions as medium platforms with 125 mm guns are supposed to be in a AT battalions in addition of ATGM carriers (instead of MT-12 towed AT guns). As is in VDV by now.
The Soviets/Russians used tanks in recon units and anti aircraft gun vehicles to increase the firepower
As did americans with their armored cavalry units
On a new brigade types (rumors from good sources but still rumors):
Heavy brigades will have all armata based vehicles from MBT through IFV to command and even air defence vehicles.
They supposed to be a successors of tank brigades. Plus will be a new type of motorised infantry brigane (two battalions of inf + two battalions of tanks) which will be classified as a "heavy brigade" also, it will be a completely new experience. Seems like an tank-heavy (atleast two tank battalions per a brigade) mechanised shock units.
Medium tracked brigades will have all Kurganets vehicles including Kurganets based APC, IFV, MBT, etc etc.
Medium wheeled brigades will have all Boomerang vehicles including Boomerang based APC, IFV, MBT, engineer, etc etc.
This will be successors of motorised infantry brigades, most numerous and tactically-flexible.
Light brigades will have all Typhoon/Boomerang-10 based vehicles.
And Tigr/Wolk based. Look at the Spetsnas in Crimea with their Tigrs and trucks, they are that is called "light brigades" (as some mountain troops units are). Still they supposed to fight on foot, not like heavy and medium brigades, which rely on their IFVs much. They are for specific tasks only, not for common combined arms battles.
Plus VDV seems to be on they own in case of organisation, not fitting in any of the brigade types (it seems that several "air-assault" brigades and regiments will be armed with boomerang class vehicles and will be a "russian Stryker brigades" as they are now).