I think it’s generally a good idea.
Worst-case scenario, you delay your enemy another second, which isn’t a huge benefit, but isn’t a bad thing.
Best-case scenario, your enemy is entirely rage-drained by the time they get to your kill island, and are easy prey.
They often fail to rage-drain your enemy, but they can easily force most dragons to spend a little rage (or start a spell cooldown), and if your timing is good - or theirs is bad - you can put some serious hurt on your opponent.
So basically…it won’t always help much, but for the cost of a couple level 1 mages, it’s well worth it. In my opinion anyway.