I can understand why that objection would be raised, because lexical binding is slower in code that is interpreted rather than compiled, compared to (shallow) d

I can understand why that objection would be raised, because lexical binding is slower in code that is interpreted rather than compiled, compared to (shallow) dynamic binding. Under shallow dynamic binding, there isn't a chained dynamic environment structure. Variables are simply global: every variable is just the value cell of the symbol that names it. The value cell can be integrated directly into the representation of a symbol, and so accessing a variable under interpretation very fast, compared to accessing a lexical variable, which must be looked up in an environment structure.