The overload mechanic needs some rework.
It has potential, but the short range, easy to interrupt, the time of the channeling and the attunement lockdown is extremely forbidding for a frontline ele.
My suggestion would be, let eles cast spells from that attunement while overloading it.
Remove the channel, make it an effect on the ele.
On top of that, make it so the ele NEEDs to cast spells from that attunement to overload it. So to interrupt an attunement overload you need to make the ele stop using skills for (?)2secs (long stun or stunlock).
This would give more gameplay to the tempest, not locking it as a moving target for 5 secs. It would let the tempest do something for the duration of the channeling, include dodging. It would also make overloading an attunment more interesting, where you need to keep your attacks going to get that attunement overloaded.