I hopefully did explain my reasoning in my previous post earlier in the thread, but I'll briefly do so again in case there were parts I missed addressing or in case people haven't read it:
I think that the content releasing buffed and getting nerfed after a few weeks has the potential to alienate mid-tier-and-below guilds who will have their natural progression severely disrupted (or effectively reset depending on how you look at progression as a concept). If a guild is 4/9 hardmodes in Ulduar and progressing their 5th, nerfing the entire raid by a drastic amount as was done in Sunwell would see that guild suddenly breezing through the majority of the hardmodes, effectively compromising their entire progression.
Given that Onyxia's focus is delivering the feeling of progressing through the expansions, it seems to me that deliberately interfering with the majority of players' progression would be in opposition to the focus of the server - or a disaster, as I put it.
If the goal is that more of the population gets a chance to complete the content, then ultimately I think "a brief chance for try-hards have a go at pre-nerf values" is not worth compromising the progression of everyone who is mid-prog when the nerfs are implemented.
I found the three Frostmourne seasons very enjoyable and a suitable challenge, but I would believe that data exists showing the wider population would not agree. I just think it would be better to keep the difficulty the same throughout, whatever level it might be.
Hopefully I've managed to articulate my points a bit better now. :)

