You will always need a main battle tank for the foreseeable future, or at least something like it. Something that can deliever massive damage but can also take something. Even in "tank-unfriendly" countries like Afghanistan, an MBT can sometimes be very useful. Read the USMC reports. The tank REQUIRES the "Colonial-Skirmishing" enemy to either massively attack the tank (good luck if THIS one is well supported and has passive + active defense systems) or bypassing it. A tank can close off a lot of areas / certain positions in such "countries" ... A wheeled tank with 120mm has also its advantages - lower logistical footprint, less maintance/equipment costs, much highter strategic mobility and even tactical with good road network but in the end especially if all passive and active protection systems fail it can't take the tougher hits.Iran's Army has a great need for modern Main Battle Tanks as demonstrated in both the Iran Iraq war and more recently during the Syrian Civil war. There is no substitute for Main Battle tanks.
Iran needs ca. 600-800 MBTs imo, same quantity of TRACKED ifv which work together.
Americans will cut, like Russians and Chinese too, their numbers.
You aren't "allowed" to have too few but too many (always active, I don't speak about save guarded reserves ), cause too high costs and no need as long as not active war.
Check out Israeli Army lul.
10 active Brigades.