Early (pre-8.0) Tcl was also literally string-processing the scripts. 8.0 brought a byte-compiler and the TclObj internal structure that maintained “native” values for types (I.e: a value “1.2” used as a floating-point value had its value cached as a float/double, versus reconstituting it from the string “1.2” every time it was needed. Note too this conversion happened nearly 20 years ago[0]. These days there’s some excitement surrounding the byte-compiling targeting LLVM[1], so faster still...
Early Tcl was slow - but it was being compared to pure C. Recent Tcl is as snappy as any HLL.