Both of these do not apply to heroic Odyn.1) no video guides to carry your ass 2) No idea what the bosses do.
The mechanics of the fight are very, very simple. On HEROIC ( which is the "normal" difficulty functionally where most average guilds should be expected to clear the content with reasonable effort) Odyn with 21 players has 1.25 billion health, two adds that have 500 mil health each that need to be dpsed to 25% ( without the ability for most classes to cleave them ) and an additional set of ~6 adds that spawn twice before phase two. On phase two the two 500 mil adds come back one at a time with the extra adds again (given you only need to dps the big ones down by 15% each time) with a healing check comparable to mythic ursoc. The vast majority of these adds cannot be efficiently cleaved.
The sheer amount of damage required for a heroic fight is asinine.
Mythic Ursoc has 1.3 bil health with an add that might as well not be there. Even then, the fight wasn't a walk in the park for the best guilds on the first lockout of mythic EN.
You're applying a false equivalency between heroic Trials of Valor and mythic EN. Just because mythic EN was, perhaps, too easy, doesn't mean that heroic Odyn should be harder than half of the raid on mythic to overcompensate especially considering the ilvls rewarded. Additionally, It isn't a surprise that emerald nightmare isn't a difficult raid. I think this is somewhat intentional and precedented as it isn't an important lore raid that involves an important villain. You can liken this to highmaul in WoD or MSV in mists. Typically, blizzard reserves the first raid to be fairly tame and then piles on an actual hard boss or two at the end of a tier.EN was a joke raid, and the numbers prove it; 1st and 774th(number of kills atm on wowprogress) Xavius Mythic kill is 41 days. Same rank time gap for Archimonde Mythic was pretty much 6 months(179 days). Keep in mind the guy's guild being 4/7 puts them somewhere at world rank 1500, so idk what you expect from them with performance in a new raid, but that is low.
Blizzard introduces a non-ezmode raid and idiots with no clue what to do go in expecting faceroll just because they killed the 4 easiest mythic bosses of a joke raid and wipe for hours? Well no fucking shit.
I think heroic Odyn is harder than most mythic Siege of Ogrimmar bosses and that was one of the hardest raids ever made especially before blackfuse belts were nerfed.
The main reason why EN is considered easy is purely because of Xavius and has no implication on the previous 6 bosses. This means your attempt to compare the first 4 easy bosses of mythic EN to heroic ToV is even more fallacious.