[grzm]

I didn't mean to imply that you said it was a weakness, though I did think some may consider it as such ("what, you don't have enough self-control to limit your smartphone usage?"). I'm addressing the fact that self-control is not limitless (even if developed and increased) and that if one's goal is to be more productive, one should feel free to use the tools available to them, which include both modifying one's environment and increasing self-control. And of course any modifications have to fit in with how you want to live your life. If it's crippling, it's not a useful modification. Having a dumbphone may be crippling to some, and liberating to others.

You seem to have dismissed the former entirely with "that doesn't seem sensible to me at all", and here leave it as only a last resort. I don't believe that's a useful way to view it. Use the tools you have available to modify your behavior.