Most of the time you throw grenades, but sometimes you want to throw a molotov coctail. The molotov coctail is situational. It should not be the first thing that the soldier grabs when you press to ready a grenade. Now if you got molotov equipped everytime you want to throw a grenade you first get molotov, then the grenade. I repeat, the molotov is situational and should be at the back of the grenade rotation.
I did some testing and molotov is ahead of explosion pack but behind ordinary grenade. Molotov should always be last.