I see not a single guild has fully completed both 8m and 16m NiM EC. A lot of the discussions have been based on assumptions, second hand info, past encounters, partial operations. Of course it leads to comments and opinions based on partial facts and individual experiences. And therefore the divided opinions. When a guild eventually clears both 8m and 16m, I am sure more respects will be given to their feedback.
No disrespect to 16m groups, but I can understand why some 8m players don't accept the current feedbacks that 16m contents are harder at this stage. The following may explain why.
Before our guild stepped into 16m TfB HM, I have been reading on the forum how the 4th and 5th bosses are miles more difficult than 8m (those posts should still be around somewhere on the forum). We eventually found out that 1st, 3rd and 4th bosses in 16m to be easier. We did switch to 5 heals for a smooth run with 2nd boss. And we found the final boss to be slightly harder. We had a few wipes while the tanks working on holding the aggro and we experimenting the number of dps on anomalies. Saw one enrage before clearing it.
Another reason might be that progression is harder on everyone's first clear. 8m group clear 8m content first and then found 16m easy subsequently. 16m group clear 16m content first and then found 8m easy subsequently.
Our guild has done both 8m and 16m NiM EC (we have 4 distinct raid groups, 3 of which are 8m teams... roughly 50 active progression raiders give or take). Everyone agrees, the difficulty in 8m is a joke and not even comparable to 16m on the first two bosses. Not enough info to comment on Kephess yet. Vorgath is of course easy on both.
Any 8m raider who still clings to their skepticism simply hasn't experienced 16m tanks yet.