That is not the case unless the +healing of the druid is a hell of a lot better in comparison to the spell damage of the DPS casting the DoTs. Now, if you take into consideration the amount that is healed by a Rejuv spell followed by a swiftmend right before the Rejuv ends then you can probably do that easily and especially if the swiftmend crits.
However, this is why swiftmend has a cooldown and it is also why the amount of +healing needed to pull this off against equally formidable opponents is so much to the point where you can forget about acting as a Healing/DPS hybrid properly. It also means that the rejuv must last the full time period for it to tick which is asking a lot in the arena. You can still be very effective due to Roots, Cyclone, and the run speed increase though which allows the druid to take advantage of the whole idea behind HoTs which is time itself.
Thus, my belief is that if you wish to nerf druids then nerf the speed (which they did) and nerf the CC abilities. From there, the skill of the opposition should be enough to bring druids down to a balanced level. On top of that, it will not effect PvE nearly as much since our CC is nearly useless in almost all dungeons and raids.
That plus you already mentioned that LB does not permit swiftmend anyways.