I had a whole semester worth of Squeak at Georgia Tech. Can't really remember much at this point except that everything was an object and the environment we worked in was super slow.
Of course, some of the extra performance is lost when new layers of code get added, specially in the graphical user interface.
The UI conformity requirement has loosened up a lot with the web and web apps, but I guess that the time is still not right.
It is objectively slow, but not slower than full featured IDEs like Visual Studio or IntelliJ, which offer a much more constrained environment and toolset.
Python is also “slow” and we still use it.
BTW, it’s nice to talk yo you again, Jecel.