They wouldn't remove the reward, they may lessen it, alter the distribution and put more of a lump sum of myth on the last boss, but they wouldnt render the first, or second boss completely void of myth reward. That's part of the incentive to even do the dungeon, is the progressive reward that comes with completing each stage. Regardless, you can still clear the entire dungeon in about 9-10 minutes anyways.

Just to be creative, because why not. A more interesting method to 'fix' that type of scenario, would be to place a permanent regen on every single mob in the instance, excluding the bosses themselves, or including, whatever. That serves two points.

First - it makes burning a little more difficult because the hp restored between spells may just end up being enough in some cases to warrant an additional spell to be used, which can slow down the burn.

Second - if a mob is on the hate list, but remains at full health for more than a few seconds, it automatically resets and goes invulnerable, returning to its normal roaming point. Now, dots would work to do the same thing, keeping them claimed while the dot worked on the mobs, but at the same time, you're actively engaging the monster, building the LB gauge by actually participating in combat, even if you are running away.