I'm hating it, i think its one of the worse decisions they could make.
They are repeating mistakes that they already had in the past and they were able to solve, just to go back and making it again now.
Tiered raids is a mistake, it already failed in TBC and it is failing again. Less and less people are raiding each day.
You seem very confused. No-one is talking about tiered raiding. The discussion is about having a single raid with a linear boss progression path. In fact I'm not even sure what you mean by "tiered" raids. Every WoW expansion and vanilla has worked on "tiered" raiding. The higher the tier, the more difficult the encounters and the higher the gear requirement. It's always worked that way. And in fact the ONLY raids in TBC with a linear boss progression path were Gruul's Lair (only 2 bosses), Mount Hyjal and Sunwell (ignoring the key/quest/attunement requirements, which again aren't relevant to this discussion as ToT doesn't have any of those). All of other TBC raids (in their own right) had either different wings or optional boss kill orders to some degree.
As for the actual question, I like the linear style. Makes it feel a little bit more epic and does't allow guilds to skip "hard" bosses.