Hi ESB! Happy to help you walk through why each answer choice is correct/incorrect on this one
Since this is a Most Strongly Supported question, the correct answer choice will be strongly proven by the facts in the stimulus. The other four answer choices will not be supported by the stimulus (such as an answer that is exaggerated, or one that provides information not contained in the stimulus).
Similar to your explanation, answer choice (A) is incorrect because it contains comparative language not contained in the stimulus. As you said, the most that we know is that these designs typically turn out well.
Answer choice (B) is correct because it is essentially a restatement/combination of several ideas contained in the stimulus. From the stimulus, we know that designs that turn out well (AKA good designs) go through many drafts, and that sketches of the design allow the designer to see flaws in the design and then allow them to revise the design. Combining these facts, we arrive at answer choice (B), that many designs that turn out well were originally designs that were flawed. Unlike answer choice (A), the word "good" in this answer choice does not go too far and can be viewed as synonymous with turning out well.
Answer choice (C) is wrong for a bit of a different reason than what you said, but you're on the right track here. From the stimulus, we only know about designs that typically turn out well, but nothing in the stimulus tells us about characteristics of designs that do not turn out well. Since answer choice (C) discusses designs that do not turn out well, it cannot be correct. Additionally, as you mentioned, the stimulus uses the word "typically" and the answer choice is more absolute than this, meaning it cannot be supported by the information in the stimulus.
For answer choice (D), your logic is definitely right here, but just to spell it out a bit more: the stimulus doesn't tell us anything about how the initial conceptualizations of a given design influence how the design eventually turns out.
Finally, for answer choice (E), your logic was on the right track here as well. All we know is that each sketch allows the designer to see the idea's advantages and flaws, but we do not know whether there is another way for designers to see the pros and cons of their designs as well.
Overall, great job with your reasoning on this question, and I hope this helps!