That makes sense. If you look at the Record Sheets, it even arranges it like that.
Battle Armor Squads/Points are required to be the same model, which is why they need that multiplier. Their Record Sheets reflect this, even the Alpha Strike cards.
ProtoMechs are not required to be constructed of the same chassis in a Point. Other than for activation purposes, ProtoMechs operate just as alone as any 2 Combat Vehicles in a Point would. Their Record Sheets reflect this, even the Alpha Strike cards.