Ah, it's refreshing to know that there are people who voluntarily learn all that stuff I worked so hard to forget! The point being that mechanised infantry probably could do all of that by themselves (since it requires in essence being relatively agile and being able to fight once contact is hit), if they had helicopter cover to provide Excessive Force (the basic function of the tanks) where required. Obviously, they'd need a lot more helicopters than are currently meted out - the one regiment per brigade that we have nowadays simply couldn't be in enough places at once to do that. It's not that they do'nt have distinct roles nowadays, it's whether they need to stay like that.
That is an interesting perspective - but I would argue against it as simply increasing the quantity of helicopter forces wouldn't be of assistance in certain kinds of ground operations. This is particularly true if the enemy unit [say, a division] has an intact and sophisticated anti-aircraft brigade.
In any such maneuvre the apaches would first need to fight a separate battle of their own against the enemy air defence assets, adding an additional level of risk and complexity to the firefight which could leave ground forces unsupported while the Apaches fight the anti-aircraft brigade. Note that the Apaches would probably lose such a fight, or at best be impeded and tied down, which would leave the mechanised infantry unsupported at the critical moment [such as a breakthrough operation].
Mechanised infantry alone don't have the organic firepower or survivability to break into some kinds of enemy defensive system and roll through it and out of it. In some circumstances they would therefore be dependant on the Apaches/tanks to fight alongside them. But it would be unwise to feed pure mechanised infantry brigades to an enemy formation on the premise that the Apaches will always be able to keep up. This is not simply a question of adding more numbers of helicopters [bad weather can prevent effective flying, for example]. And modern anti-aircraft systems will really ruin your day - which is one reason why helicopters tend to be given their own missions, in parts of the battle space that have been prepped by intelligence and which are known to not be saturated with air defence.
Obviously, tanks are not limited by such air defences and can strike at them and eliminate them with near impunity.