I'm not so sure STO stole ideas from Curtis. Their design acutally looks closer to the Defiant class, they just added some pointy things and changed the angles of the hull. DJ Curtis actually re-envisioned it and the Valiant looks like the Defiant class only in general form: low profile, broad, one piece hull, etc.
That being said, I actually don't find either particularly attractive, and I prefer the original Defiant class over both of these.