I would say that a Fire/Storm SHOULD take RoF for use against AVs... but if they don't, it's not a great deal. The reason is that they do far less direct damage that benefits from Containment, than pet damage that does not benefit. You will have 3 Imps, 2 Tornados, and 1.5 Storms out on the average, and that puts out significantly more damage than the Controller's direct attack cycle. Not to mention that all of these powers plus Freezing Rain suck up endurance, and that if you are soloing the AV, you need to run defensive toggles in addition to having some IO set bonuses, since Fire/Storm has no taunting pets. So... due to Endurance problems, I don't think that a max-damage personal attack cycle will be that useful, compared to the much more End-efficient summons.
You may still want RoF to help with a bit of damage, and to keep the AV in one spot. Otherwise you have to run Hover to stay away from melee AVs.
Yeah and how are you going to keep that AV in Tornados, Freezing Rain, Bonfire and Thunder Storm?
If anything RoF is even more important that usual for Plant/Storm since it relies so much on damage over time effects.
Your taunting pets makes me wonder about the viability of a Dark/Storm.
You get the Immo and the taunting pets plus the damage. Plus Dark Has better access to IO sets then Fire.