Hopefully this reply isn't too late to make a small amount of difference. I'm a relatively new player myself. I've owned the game for years but haven't really put any time into it. I started out rolling thief because that's been my go-to class in every MMO I've played. But I underestimated how difficult it would be to compete with the established playerbase in WvW and just quit the game once I hit 80. Came back a year or two ago and decided to try Revenant because it looked cool and the moveset seemed to suit me. That class turned out to be even harder for me to perform with in WvW because it has like zero escapes (at least that my noob self is aware of). So I'd either have to win a fight or die, and I certainly wasn't winning any fights.
Now I've come back to the game once again to try out the expansion and I'm back on thief and loving it. Unlike my last attempt at WvW roaming, I studied a bit of gameplay from good thief players and tried to emulate their tactics. I've been MUCH more successful in one-on-one fights and with escaping fights where I'm outnumbered or outskilled. It was definitely unexpected and a nice surprise to actually start getting some kills. What's been great about playing thief is that I can disengage pretty much whenever I want. I'm spending a lot less time running back from my waypoint.
As for PvE, I've done just fine in open world with a power daredevil staff and dual pistols. I found a low intensity build guide that has made the open world stuff a lot less annoying. I highly doubt it's meta, but it's not proved to be an issue thus far while doing the HoT and PoF stories. I plan on gearing up for some meta Spectre build next so I can engage in the group PvE content down the road.
Again, these are the ramblings of a newb, but I feel like I've shared your same viewpoint in the past. I don't have enough knowledge of the game as a whole to say whether or not thief is in a good or bad spot.
TLDR; Fully geared my thief years ago in ascended and tried WvW, got stomped and quit. Came back this year, tried playing with a bit more tact while 'copying' better players and found much more success.