My only assertion was that IS is highly underrated for SFs
Possibly.
and it is one of the core skills for that positioin.
Again, this one really depends on too many things. I personally put jump shot, outside defense and inside defense as the core skills to the position. But really, on a high level SF it would be ideal to have everything. So I guess it really depends on your definition of "core".
Run of the Mill Canadian Manager