Not sure I agree. You can "blind type" on a physical keyboard, and even if it has less sophistication in the way of inputting large amounts of text (lack of auto complete, lack of fuzzy typing/auto correct), a calculator is purpose built with tons of shortcuts and contextual menus that you access from muscle memory without second guessing yourself. Right now, if I've got a mildly complicated mathematical expression to type, I'd rather do it on a last-century calculator rather than e.g. on Android's GeoGebra.

It's been a long time since I've done it, but I could type pretty quickly on a TI-83 - even with the silly ABC keyboard layout and all.