On 2/18/2018 8:04 PM, John B. wrote:

So, one might say that for riding in hilly terrain the STI shifters
are mandatory for success while if riding on level ground are far less
important.

Even in hilly terrain, STI is not mandatory for non-competitive success.
I've crossed the Appalachians with friction shifting.

People succeeded in riding in hilly terrain even before there were
derailleurs, let alone STI.

--
- Frank Krygowski