Technically, you are correct. However, Smalltalk was the first language to popularize OOP and is widely regarded as the gold standard of OOP implementations. That’s why it (and not Simula) has served as a powerful influential force in the design of modern OOP languages such as Dart, Groovy, Objective-C, Perl 6, Ruby, and Scala.
You’re also right about the early days of Smalltalk. However, modern Smalltalk is plenty fast. Companies like GemTalk specialize in selling high-performance Smalltalk solutions to the enterprise. Smalltalk MT is a very fast implementation for Windows. Pharo is actively working to optimize Smalltalk performance. These are very good days for Smalltalk, which is why I’ve been a strong advocate for the language.