Thoroughly enjoy it.

Uh. Thanks... for the warning, I guess? What warning are we talking about? Is this like Revenge of the Body Snatchers and I haven't become "we" yet?

In my experience leveling my alts, I've just done the planetary arcs and the class missions. I haven't done any flashpoints or side quests on the majority of them. I've found myself to be almost an entire planet ahead of the curve as far as my level goes. However, if you were just doing your story quests and absolutely nothing else and found yourself in a bottleneck, do some tactical flashpoints, heroic missions with your companion on a lower level planet, or go back and do some of the side quests. While it is true that they've increased the experience gain overall for planetary and class arcs, that doesn't necessarily mean your experience is going to be ideal or on par if you simply do the bare minimum. Go back and experience more of the content.

I just got this game a week ago, but I had friends that already had a pretty established guild, so I was put in there from level one. I'm still not fifty yet, but the majority of the guild I'm in is fifty and they frequently run hard mode flashpoints and are starting to do operations regularly. However, they ALSO get on alts to help me level when they're not doing stuff on their fifties and will do flashpoints with me around my level, help me through heroics, etc. So, what it sounds like to me, is what others have already pointed out; you're your own worst enemy. You're fifty and the rest of your friends aren't, and you don't want to abandon them but it also sounds like you're not really putting forth the effort to help them level. If they don't level as fast as you want them to, then you'll have to put up with it, because they're entitled to play the game as they wish and level at their own pace. I'm certain there's classes you haven't played to completion yet, so just make an alt and help your guildmates/friends get up to fifty so then you can all experience the stuff you want to do. Also: the game's been out for a little over a month, and within that span they've already released Kaon Under Siege and expanded Karagga's Palace. I don't know what exactly you're expecting in terms of flow of content, but if you're already hounding for more content, it might be time to take a break and do something else.