I played WoW from day 1, until the end of Firelands. Just to qualify my opinion as not completely bs, but only just partially instead
Later arena, but first BG's started to push people into instanced, reward-based pvp and killed world pvp. That's completely true. However, the game probably wouldn't have thrived on Southshore-Tarren Mill battles quite as well as it did on BG's and arenas. While instanced pvp was bad for nostalgia's sake, it was good for the growth of the game, as the subscription numbers would indicate.
People who don't like the accountability of arenas but do like to pvp often complain about how arenas are killing bg's. People who hate the large team size and diminished personal impact of bg's but like to pvp often criticize bg's for not highlighting personal skill the way arenas do. People who like pvp but don't like the accountability and tight coordination of arena, but also don't like the loose coordination of bg's tend to criticize both for having killed world pvp. In the end it's all very cyclic.
WoW is a big money grabber. PvP and PvE could easily use the same armor, but to be the best you must grind for both types, and spend monthly. I used PvE armor on my Cata Pally in 2v2, and usually whooped ass (I think I did 53k DPS on Morchok, but cant remeber)
I used to be a hardcore WoW player, I was in DnT (death and taxes) until the guild broke apart. Then I found various homes raiding. The thing I HATE about arenas is that in any bracket 2v2 3v3 5v5 there are always flavors of the month. Back in BC Resto druid Arms warrior made up the top 10% of comps in the 2v2 and 3v3 brackets. I feel it was broken. But then again one could argue Raid gear being allowed in PvP was unfair too as Pre BC on my priest I could one shot people with a crit smite or holy fire. All Bgs and Arenas are fun, you just have to remember its a game. . .
However some of the most fun I ever had PvPing was at Tarren Mill..... Huge gank squads and such. I miss the good ole days.