If you hold Fn you get the traditional row of function keys, which seems like a pretty good tradeoff. And if you really hate that, you can simply configure the touch bar to always display them, in which case literally the only downside is that they are not physical keys anymore. Do people really touch-type the function keys so heavily that this becomes a an actual annoyance and not just an ideological one?

Adding an extra row of physical keys that do the same thing as the row of virtual function keys, at the expense of trackpad size and possibly ergonomic (harder to reach the touch bar) doesn't make a lot of sense IMO.