This isn't about what is a more worthwhile endeavour: PvP or PvE. In my opinion, if you want to spend endgame raiding, that's fine. If you want to spend it PvP'ing, that's fine too. This is a discussion of two fundamentally different reward systems. One where quality varies with challenge/skill (Quality System), and the other where quantity varies with challenge/skill (Quantity System).
One of these is a better system than the other. I believe that the Quality System is superior because we tend to value quality more than quantity. Because it has a better natural, even progression. And that it leads to better gameplay and encourages people to constantly improve, while the Quantity System leads to unnatural and counter-intuitive gameplay.
But clearly, many of the commenters clearly don't feel the same way. To them, the Quantity System is superior because it allows people to reach parity gear-wise faster. It also means that all progression options for your character are within reach. You'll never reach a point where you just cannot improve your character because you can't meet the challenge.
It's fairly easy to use either system in PvP or PvE. For PvP, simply slap Rating requirements on the gear. Boom, there's a Quality System in PvP.
To implement a Quantity System in PvE, we could assign ratings to each boss. Attumen would be a 1000, and Illidan would be 2400 or so. The other bosses would be scattered along the spectrum between them. Each week, a PvE player gets a rating equal to the highest rating of a boss defeated that week. For example, a raid that kills Prince Malchezzar might get a 1400 rating. On Tuesday, the Consortium gives you a certain number of Raid Points depending on your rating. You then use these raid points to purchase rewards from the Consortium.
Bosses no longer drop loot. Maybe you could get a title for defeating specific high-end bosses (Coriel the Dragonkiller Killer). The only result from downing a boss is an increase in rating, if the boss had a higher rating than your current rating. Your rating would reset to zero on Tuesday. Every so often, perhaps with the PvP Seasons, Blizzard introduces new raid gear which you can purchase.
Now, there are some fine details to work out. PvE is not quite as granular as PvP, and you can't do swaps as easily, so you have to somehow account for people who sat out that fight. And ratings would inflate over time as gear makes the challenges easier, and would have to be readjusted when new instances came out. But that's a basic Quantity System implemented in PvE.
Is that a better system than we have now? Maybe. I don't think so, however. I think it would lead to stagnation for a lot of guilds, as they would reach a "comfort level" of farming and refuse to try higher bosses on the grounds that the additional rating would not be worth the time and effort, the same way that some people prefer to lose Battlegrounds fast rather than go for a drawn-out win.
But everyone else seems to be solidly in favour of the PvP Quantity System, so maybe we should leave PvP alone and change raiding to match it.