Skulker said:
I start with the assumption that Canon know a lot more about making cameras than I do.
That's the spirit, I'll remember to nominate you for the "Canon compliance of the year" award

... but you're correct, not every design decision is "crippling", but as it happens this one is different because ML has proven that auto iso with flash is no problem at all - you can use other iso settings manually, so there is really no reason why the camera shouldn't be able to select the iso according to the ambient light as usual and then let ettl decide the rest.