Absolutely. This article is reminiscent of the type of brief tutorials from the mid/late 90s in QBASIC newsletters introducing how to use ASM to get speed gains

Absolutely. This article is reminiscent of the type of brief tutorials from the mid/late 90s in QBASIC newsletters introducing how to use ASM to get speed gains, with all the associated assumptions. The concept of "lowercase" breaks down terribly once you go beyond simple A-Z. You can apply similar rules to certain limited code sets, but a universal tolower() won't work so well with this method.