Another major problem isn't that they're twinking at 49. Really, the bolster buff is so broken if you twink at lower levels, your skills hit even harder (It's designed to make up for the lack of utility/spec options at lower levels by making the few skills you do have access to, hit even harder! Thus why opting out of chosing an advanced class for a particular amount of time makes you extremely scary). We've got a group of 2 twink-sins an OP, and a jugg that run around at level 21. They've been there for about a week and a half. They're actually nastier than the 49's. A 4-man sorc team, same thing (They've been around for about 3 weeks, but I have rarely seen them in the past week. Still the same level though): They spam force lightning (Does about 1k a tick on you) the entire game, walk away with 350k'ish damage done in the WZ about 175k healing done. Dominate everyone. The level 31 modded gear from the Cartel Market has made the 31's a nightmare. They'll stay at 31 for weeks, you'll get into back to back to back games vs those players and while you're leveling up - They're not.
I have no problems with people, who aren't using exploits to stay at level 49 perpetually, twinking their toons with the best gear they can. None at all. This is totally within normal game mechanics - there will always be people who put the time into maximizing their gear, and it's something imo that should be a part of all MMOs - PVE and PVP.