Back in Season 8, there was a distinct division between the Hardcore and the Casual PvPers. The Hardcore spent most of their time in arenas, as the only way to get into the best gear possible was to save up arena points and hit 2200 rating. Of course, at the very end of the season all the Wrathful gear became available for honour points (excluding the 2200 weapons which had to have been earned during the season), but for the duration of competitive PvP, arenas were where it was at.
The Battlegrounds, while certainly played by Hardcore and Casual PvPers alike, were a place of casual, for fun, play. Sure, you earned honour with them, and you could use that to buy epic gems and make a bit of profit, but once you'd gotten all your honour gear, BGs became sort of useless. The lessons they had to offer were learnt only during the very rare premade and even then it was always against PuGs, thus a distinct lack of challenge.
Arenas and PvP
Arenas still offer the best rewards in the PvP world in Season 9, but with one key difference. You can run Rated BGs for the same rewards. Running Rated BGs also gives you access to the old PvP titles, which have been brought back for Rated BGs. Running arenas all the way up to 2200 rating will net you the best weapons, once they come out, but they won't do much more than that, since rating below 2200 doesn't get you anything, except 1500 which gives you extra Conquest Points every week.
But outside of material rewards of arena play, what do they teach the PvPer? Lots about how to take down an opponent 1v1, and how to win in small-scale PvP. But they don't really teach one of the most valuable lessons of large-scale PvP. Teamwork.
Rated Battlegrounds, and Teamwork
Now before all the arena junkies out there gut me, don't get me wrong. Coordinating with your arena partner, or partners, takes teamwork. I am absolutely not belittling that fact. But it doesn't teach the kind of teamwork I'm talking about here, and that's the kind that, to borrow from the other metagame, you learn by raiding.
Raiding requires a pile of coordination. Your RL has to be able to keep 9 other, or 24 other players on track for several hours while you down bosses and battle mechanics. Rated BGs require a similar amount of focus. You have to keep 10 players together, and keep them so together that they co-ordinate better than the other team. It becomes much less a game of gear (although gear does matter, to a certain extent), and one of pure skill.
In a Rated BG, if you don't have tactics, you don't have a strategy, and you don't have micro and macro-management skills you lose. Plain and simple. Because you aren't playing a herd of unorganized PuGs. You aren't fighting a pre-programmed boss. You're playing very real, very smart, human opponents. They've got an organized team, that uses teamwork. You need to have one that has more.
A Shift in the Spectrum
The point I'm trying to get at here, is that the whole landscape of PvP has changed forever. With arenas now, in some ways, a side game played to get Conquest points for gear, Rated Battlegrounds have become the site of hard-core competition. Players are judged on their RBG rating, and the 3k+ players who have already topped the ladders are mini celebrities.
PvP is no longer about your ability to burn down that stupid disc priest and rogue and mage buddies. It's about complex coordination between teams. It's about more than just having the fastest reflexes. It's about strategy and teamwork.
With all that said, it's more important than ever before to work together effectively with your team when you run Rated BGs. If you're your guild's RL in RBGs, then set up some training runs, get your guild used to focus firing, to coordinating crowd control, and working as a team. The season is still relatively young, and Rated BGs are something brand new to the WoW metagame.
In a couple seasons, incredible Battleground coordination will be par for the course. While everything is still being tried and tested, in other words right now, is your best chance to get really good at Rated BGs. And really, you've only got two choices, catch up and learn some serious teamwork fast, or get left in the dust.