The big issue here is there are 2 completely different scenarios resulting in the same 72 hour ban.
Scenario A) People undermanned the fight and killed flame leviathan in his area using no exploits, just killed him with proper kiting/good dps.
Scenario B) People pulled Flame Leviathan through his wall when he had 4 towers up and killed him outside without having to deal with any of the adds/etc in that fight, and without him resetting; which is supposed to happen upon the boss leaving his spawning area.
It is completely unreasonable that Blizzard would punish players for using tools which were given to them to kill a boss in a manner such as scenario A. No glitching, no nothing, just "this boss REQUIRES you to kite him, so if you can kite him well enough within the game's own mechanics and intended fight area, AND do enough dps, you can kill him."
Scenario B on the other hand, is a different story altogether. Players who killed FL in a manner which is INTENTIONALLY pulling him to an unintended zone to fight, as well as getting an unintended amount of attempts to kill him before his health resets deserve the 72 hour bans.
In conclusion, I think those who got banned for pulling him out of his zone with 4 towers up, etc were definitely exploiting intentionally and deserved the ban.
Those who just undermanned the fight and still killed him should not have had any actions taken against them as it is not their fault that Blizzard themselves made the fight just_that_easy.