A medium brigade fighting a conventional enemy brigade for instance... the medium brigade has 25 ton vehicles protected from a range of threats with vehicle armour protecting from a range of enemy vehicle mounted weapons... both guns and missiles.
Perhaps one should ask the question, can a tracked or wheeled 25 ton vehicle with advanced ceramic armour and NERA, and of course Shtora, APS that will stop APFSDS rounds, and Nakidka to make lock ons difficult for thermal guided weapons like Javelin going to be protected...
Lets take a US unit... 120mm smoothbore on tanks and 25mm autocannon on IFVs and TOW II ATGMs and Javelin ATGMs. Assuming the APS is effective and the 25mm autocannon is not effective all the vehicles in a Kurganets unit should have reasonable protection from anything a US equivalent could direct at it even though its MBT is only 25 tons and presumably has a fire and forget tube fired ATGM.
In most operations... and we are not really considering WWIII though it should apply there too... the enemy will have a fairly conventional force of MBTs and IFVs and APCs and a multitude of other light vehicles in every unit. Previously there was no heavy unit so the vast majority of vehicles are light armour or soft skin vehicles... even light brigades equipped with Typhoon will be better armoured overall than this, with medium units having much better average armour even if modern enemy MBTs will have better protection all the other vehicles will be better protected than all the other vehicles in the foreign unit.
The whole concept is to reduce the logistics tail and prevent a situation where vehicles with lighter protection can be picked off leaving the heavier vehicles isolated.
Mixing the vehicles ruins both reasons for creating vehicle families in the first place.