You know, I do agree with you to some degree there - but then again, I'm still going to train lots of JS this season.
There are some caveats, though. It's JS for Forwards, so IS does get some boost. Four of my trainees are Forwards (or, rather, should become Fs this season; they are nominal Cs). Two of them will cap during or after the season. And I've never really trained their JS before, except for the odd All-Star week when I did not have to train Stamina.
So why am I doing this? Well, I'm finishing off my two PFs so they can also hit mid-range jumpers. I'm not mindlessly pushing the skill, I'm trying to get another matchup advantage. Prolific JS or so will totally be enough for me there. Also, my SF trainees who got their necessary C skills last season need some JS too - again, I won't push the skill beyond sensational or so. Lastly, I hope that I'll never need to train JS again, ever. Or if I do, it'll be five or six seasons from now.
Still, let's not forget that there are good reasons to train JS. It's just that people seem to see it as a primary skill for guards when it's a secondary skill for every position.