No one is going to run 8 DPS on 16 man HM DF/DP unless they are already geared out with mostly 78s, which already defeats the purpose of claiming any sort of difficulty, regardless of whether it's 8 man or 16. Hence, my point about people overgearing 16 man (as well as being more experienced) and then trying to say it's easier is ridiculous.
No that's incorrect, even for previous nim progression most of the 16 man guilds just used 8-9 DPS as enrage timers are easy in 16 man compared to 8 man. I don't know a single 16 man nim progression guild that just uses 4 healers for nim progression. Most used 5-6 healers.
As for mechanic cheesing, please explain exactly what mechanics you can cheese on those fights on 16 man that you can't on 8. Does your team magically live when standing in the laser at the end of Corrupter Zero if you have more healers on 16 man? Or if people stand in the Inferno repeatedly on 16 man? Or if they stand in the red circle on Bestia? No, they won't. It's irrelevant how many healers you have if your tanks don't understand that they have to re-taunt Draxus when he does his aggro drop or if Raptus cleaves your entire team constantly or knocks your tanks to their death. There are plenty of one-shot mechanics in HM DF/DP if you fail to do them correctly so I don't know what you are talking about when it comes to cheesing mechanics.
Corruptor Zero just has 2 add phases in 16 man hm and before the laser he has less then 10% life (6-8%). That means you could lose 10 People on the laser and still kill him easily.
Corruptor Zero has 3-4 add phases in 8 man hm, the fight last much longer (cause his has just 30% less hp in 8 man hm), and you usually get the laser when he has about 20% life left.
On Tyrans you can lose more then 8 people to Inferno. The damage on the tanks is not scaled properly, so the more people you lose on 16 man hm the easier the fight is getting (unless you just lose healer) cause the enrage timer is not existant. On my last 16 man hm raid this week i took on average 1100 damage per second on tyrans as a tank (and the other tank just took very slightly more).
On Bestia, its the same, Tanks can easily tank more then 3 Monsters cause the damage is not scaled properly compared to 8 man.
If you are talking about being able to have more healers, then you can do the same on 8 man as Nefra and Tyrans can definitely be done with 3 DPS and I'm sure there are other fights as well.
On 8 man it's possible on a few fights yes, but on 16 man you can bring multiple additional healers for every
fight. On 8 man nim tfb/sv i can't remember a single fight were you were able to bring 3 healers, which is completely different to 16 man nim.
Beyond group communication and coordination, positioning and survivability are far more important and skillful on every single player in 16 man. For example, on 16 man HM Brontes, healers can be killed instantly once the Fingers spawn in the beginning of the fight if they happen to target the same person. Also, the massive spikes you see only on 16 man are far more dangerous than those on 8 man, which is why it's a joke when 8 man teams try to complain about spikiness. Positioning is crucial in many fights especially since the areas are designed for 8 people and you have to fit in 16 people (Bestia is a good example).
In the previous tier, 16 man NiM TFB and SnV was far more difficult and I'm fairly sure it's well-known that NiM EC in 16 man was much, much harder than 8 man. So maybe 8 man was harder in the days of EV/KP or HM TFB and SnV, but I have no idea since I almost never did 16 man then. The only fights in general that are much easier in 16 man are SM ones and world boss fights like Toborro's Courtyard and the one in the Gree event.
Not if your tanks guard healers and if the healers are spreading out accordingly. Spikes or healing are not really an issue, if you can bring 3 times the number of healers (apart from Bioware screwing up damage on certain mechanics, which i have not seen this Tier at all). As long as Bioware refuses to create tough enrage timers for 10 dps in 16 man operations you can basically overheal your way through normal damage.
That leaves it to what i said before: Communication and Coordination. But in terms of your own dps/healing or tanking Rotation 16 man is nowere comparable to 8 man.
16 man NiM tfb and snv was not more difficult then 8 man nim tfb/sv. They had some twisted mechanics in 16 man nim (were damage was not scaled properly) but you also could also take additional healers to manage that. In the end 8 and 16 man nim tfb/sv were about comparable.
This tier is different, damage in 16 man is scaling properly or actually just the same as 8 man (raptus for example) and dps checks are more strict on 8 man.