I'm well aware of the icons for, say, a Sage's spells. Don't kick the GTAE, don't kick the channel unless you catch it immediately (because kicking the last tick of the channel is lol), kick the fast and slow heal. Interrupts are STILL weak in this scenario, because if I play well and kick the fast heal, it doesn't stop the Sage from shielding, using their HoT, casting the long heal, or casting the channel -- all of which are worth casting (even the HoT if he thinks he has time to use it to make his long heal crit). All I did was cost the Sage 1-2 seconds of casting, and while this can be useful if the Sage is near death, it's pretty paltry compared to, say, locking an entire school of spells out ala WoW.
Interrupts aren't useless, but pretending that they're strong is disingenuous. I have a 50 Sorcerer, I heal with him in warzones, and being interrupted is one of the least of my worries.