Pirelli MT21 is not really rally tires, its recreational tires with a catchy name. Used up a rear in less that 1 Amageza stage.
My go-to for rally is Pirelli XC mid-hard tyres. Expensive, but rears used to last about 2000 km in Amageza. Never punctured a rear, had a cut in a front from a cut-off fence pole in Botswana once.
If you run mousses in front, you could run any MX tyre in combo with a rear XC mid-hard.