I get what you're saying, and no the suit as it is now isn't slim. It would be slim on someone who was more closely proportioned to SS's OTR cut. However, I had to get it this size for my shoulders and chest. My thought was (perhaps foolishly) that since it is designed to be a slim fit suit, once tailored it would look like a slim fit suit. I've read stories where guys try to take a traditionally-cut suit and make it a "slim fit" and end up with garbage since it was never intended to be a slim-fit in the first place. Is this way off base or accurate?
I always have to get my dress shirts taken in through the waist due to my neck, chest, and shoulders needing a much larger size, and my tailor told me it's important to start out with a slim cut shirt otherwise it would never work.
I guess I figured a very slim fitting Washington would need less material removed than a traditional cut that fit my shoulders and chest.
First, I would post this in the tailor's thread where trained people have an eye for this stuff.
Second, while I would advise against massive chopping of any suit, perhaps you might be stuck with this same problem no matter what you wear. if you are that thick across the upper body and thin through the waist and torso, you are going to find suits hard to fit in general. While SS suits have a decent drop, when they say slim they mean cut slim all the way down. Looks like you may need something like a 9" drop, which you aren't going to find anywhere.
So I guess my main, non-professional opinion, is to take it to a tailor and have them pin it and see if you like the result. Good luck!