So by this logic, we shouldn't have anything other than 25 man raids. If you want 10 man, just go do 25 man with 10 people, amirite?
I know. AV is terrible.
And what ends up happening is that the population will simply focus on the hardest dungeons, pretend they're 'mandatory', and demand a nerf. You must recall the outrage at hHoR, despite there being several other easier ones released along with it.