I'd say she's top mainly because of her TAS B. The move dominates mid-long range. It's delayable, and the delaying it will add range to the attack and cause Sophie to retrack. Stepping timed for a fast TAS B may get you hit by a delayed TAS B. It seems the second 236 realigns her. This makes stepping and attacking preemptively really dangerous. Even if you step G, and the dodge is successful, whiff punishing it on reaction is difficult, as the move has deceptively short recovery. Also, it's a mid, so there's no getting around it. That's quite the threat at long range. If you aren't convinced, try it yourself. At advantage, slow TAS B catches sidestep evades and backstep evades, as well as TC and TJ for being a mid. It also stuffs step-TC harder than anyone in the game. One move. Stops your reverse mixup, outside of attacking at disadvantage... which is really dangerous against Sophie. Why? TAS B, the fast version.
You could just sit back and block it, and get a free mixup, as it leaves her in your face at -10, but her throw whiff punish iFC1BAK (76) is very strong if she decides to duck, her GI game is scary strong (thanks to... again... TAS B), and if she blocks your strong mids, she may punish you unless you opt for safer stuff... so, depending on the character, the reward for blocking the move is very small. The blockstun is also short, which is annoying. AA after getting it blocked works more often than it should.
If you're waiting, and she comes in with 236236, it's possible for her to cancel out of TAS by hitting forward (or other directions... like an RCC) and throw you. She can't TAS B and TAS cancel in the timing window. Right after the window for hitting B ends, she can cancel out and do anything she wants: guard, 66K, throw, step, whatever. The animation for TAS B is only 14-15 frames from that point. Timed correctly, a mixup between a delayed TAS B and a TAS~throw is really ambiguous. To stop this, one could try and hit her on reaction to the TAS movement, but that leaves you open to heavy damage from a faster TAS B on CH.
The rest of her tools, I'm sure everyone is already aware of. Her whiff punishing is above average, and she can do a lot of damage while being safe. Her reverse mixup is doesn't cover all options as well as some, but just her GI game and her variety of tech crouch options push it to being above average. Spaced BBs are always free, 4B gets her inside whenever. Step catching is pretty good and safe, 66A blocked leaves you in a similar situation to TAS B. 3K... safe, tracking mid kick, with a hard-to-exploit weakness to one side. BB has to be 8WR'd, it seems, and I've already talked about TAS B's tracking.
Her only problem is that if you sit back and guard, the worst thing that can happen is you get grabbed. But her grabs aren't bad. And her CF game exists. Her stage control and ringout is below average... she does have an i15 RO move though.
Idk, the risk/reward always seems to be in her favor. She punishes mid-low mixup characters really hard and out-classes most characters if they try to beat her in other ways. She has no real bad matchups, only good ones. Only characters I see as better from a theory fighter standpoint is Setsuka, Amy, Hilde. Maybe Ivy and Voldo. Idk, I think they're overrated.