>Actually writing code was never the difficult part for the majority of software created. It required skill yes, but the really hard part was figuring out what to implement in the first place.

Nah, it was mostly writing the code. One can have a very good idea of "what to implement", even on a feature by feature and architecture basis, but still need many man-weeks or months or even years with a large team to make it into code.

>Which features should the software have, how should they function and interact, which tradeoffs to make given the limitations. Stuff like that.

Stuff like that a person can sit down and plan. Which is what the techical lead or software architect role does.

They still needed to work themselves plus anything from a couple to dozens of coders to make it into actual runnable code.

If the industry was just senior tech lead roles, yeah, it would be affected less. But 95% of it is regular coding roles, even mostly boring coding roles.