Let me get this straight. If you do a Flex raid and down the first two bosses, and the third boss is giving you trouble and the raid members leave, you're telling me that I have to re-do the ENTIRE raid to get to the bosses I can loot like LFR? If Flex is above LFR in difficulty, then how is this right? How ridiculous.
Have you done it? It's literally a faceroll you can't fail, same as LFR. And no, the group I was with didn't have full heroic ToT gear. The only part that makes Flex harder is that you have to actually find people, and on dead servers that's not always easy. But the fights itself were laughably simple and the mechanics could basically be ignored for the most part because the damage was so light. We had 21 people and 3 healers, there's just no damage from any of the mechanics.
I am kinda scratching my head about the re-queueing for the same bosses thing too, would've made much more sense to just handle it like a regular raid.
Presumably they didn't want people swapping between characters constantly. In normal you're allowed to swap as much as you want because it requires you to have good gear on your alts, you can do Flex with just about any gear and be just fine. A 500 ilvl in normal SoO probably won't work so well, but 500 in flex would be completely fine.