No, we aren't the 2nd worst.
I'd say we are about the 4th to 6th worst team. What's keeping us from being a bottom 4 team is indeed our coach. His offense that made scrubby Butler teams compete with the best talent in the NCAA is actually working against NBA teams. I'm amazed at how quickly he's adjusted to the NBA. Thank god we don't have any good shooters or rim protector because we'd be a 6th seed in the East with no problems if we did. Who knows, with Zeller defending the paint (making it easier on Sully) and also running the pick and roll with Rondo, we may just end up battling for the 8th seed in this horrid conference. It's unlikely though because most NBA teams don't guard the pick and roll like the Lakers do. (like their eyes are closed!).
Teams we are better than:
-Philly- durrrr.
-Lakers- open tank job when you play Robert Sacre that many minutes vs a bottom team like us.
-Minnesota.
-Detroit- open tank job as Van Gundy aims to put decent draft pieces around Drummond, Caldwell Pope and Knight. They might creep up to a similar record to us depending on the ease of schedule.
After that, I'd say that the Knicks and Jazz are right there with us in a three team race for the 5th worst team.
What's going to help our draft position however, is the probable trading of Bass, Thornton, Turner and hopefully Wallace.
I'm still not sure what will happen with Jeff Green.
Paul George's injury and his scandal with Hibbert's girlfriend may have given us one of the opportunities that Danny Ainge waits for- a disgruntled championship impact player needing a change of scenery and coming out of contract. I believe Danny desperately tried to trade Green last year, but couldn't find any takers for any kind of decent return.
But 6 months later, Jeff Green being one of Hibbert's best buddies could be a large part of getting Hibbert over to Beantown. Danny will just have to convince Green to a friendly deal. After all we did look after him with his last contract so it's very possible. I am not a fan of Green and don't want to pay him more than $12 million a year under the new cap- but if it means getting Hibbert here and signed long term, then I guess I'd agree to it- it just means that moving Avery Bradley becomes mission number one.
Back to the OP's topic...
I'd say the answer is somewhere around the 5th, 6th, or 7th worst team. Without Stevens we'd be right there with the Lakers battling for 2nd or 3rd because our terrible defense wouldn't be countered by a decent offense. However if we trade Bass, Thornton and Turner I'm not sure how much Stevens can do to stop the pain, and by season's end a bottom 4 finish is not out of the question.
But hey, no pain, no gain. 
I disagree with this assessment. I think that from a talent perspective we are around 18th to 20th (or 10th to 12th worst) in the league. The reality is that this might be good enough to compete for a playoff spot in the weak East.
I also don't see why trading our 7th, 8th and 9th best players would affect our record all that much. I'm not necessarily agreeing that I want to see those guys traded, but they aren't close to being among our most essential players.
I can understand your perspective completely. I could obviously be very wrong. I do disagree that there are 10-12 teams that have worse talent than us.
As far as talent goes, we have:
Rondo-stud/All Star caliber (or just below currently).
Sully-stud
Smart-stud
Olynyk- unknown ceiling at this stage, offensive talent is high, although worried about his competitiveness.
Zeller- career back up big?
Bradley- career 6th man?
James Young- who knows. Good be Eddie House or James Posey- or better.
We have some picks too.
Green- above average role player? Horrible efficiency but is okay in most areas?
Bass- role player?
Bass is arguably our #1 big off the bench and gives us some strength defensively.
Thornton has average 7 points a game in 15 minutes shooting 40% from three. I'm not sure who replaces that?
Same with Turner- he stinks but he's getting 9 points a game and can bring the ball up while defending 2/3's without doing too much damage to us.
We'll arguably have the thinnest bench in the NBA if we lose Bass and Thornton because Smart and Young are rookies. Bench will be:
Smart
Young
Olynyk
Powell
Turner if he stays.
Faverani
Pressey
Our talent in particular areas is great, it's the way that talent is distributed. Like having 4 or 5 shooting guards and 2 point guards (one of whom is a D League level player in Pressey with severe defensive problems and lack of size).
Having no rim protection and no one who can create their own shot at will other than Sullinger and Thornton.
Having 3 power forwards in Sully, Olynyk and Bass who are among our best players, but not enough minutes for all of them to maximise their strength relative to the roster.
We just don't have a 'complete' roster and it's why we suck.
But it could turn the other way, we could make a trade for a half decent rim protector and another shooter and battle our way to the 8th seed with some improvement on defense.
Something tells me that Ainge won't let that happen though. He's waited so long and avoided going for a fill in rim protector that I can't see any universe in which he makes moves to make us better this season, unless we get an All Star level player at the trade deadline.
I will say that we are in a great spot for next season, when we can take a clear direction with picks, cap room and assets. Our brilliant coach just makes it better for the long haul.