Not all of my time is wasted on Reddit/HN. I actually have quite a few high-quality subs I subscribe to, and in general I learn quite a bit each day on both places from the comments. Sure there is room to cut back, but there is definitely some strong "signal in the noise."
I have felt a lack of creative energy these past few years, so I wonder if that would start to come back, but I genuinely can't picture what I'd do without those things in my life. It is very sad when I think about it, but I wonder if there is a happy middle-ground vs. going all out with a dumb phone.
I wouldn't say all of my time was wasted (and HN is the only remaining regular thing I look at, but I tend to read an article or two and comments and then be done, rather than repeatedly looking through it for something), but the vast majority was. Maybe better filtering was needed for me, and I've achieved that in other areas by subscribing to a couple of worthwhile email lists (of relevant interest areas) where I get maybe 1 email a week that takes maybe half an hour to filter and that's that.
Most of the spare time I've reclaimed is being used usefully - I'm learning Python at the moment, so I'm finding I'm doing bits an pieces here and there with that, and also I've actually made time to go back to practicing and enjoying playing the guitar, which I've done for a long time. I'm starting to feel more musically creative as well, which is definitely a change from the past few years - I had thought that it was all gone, so perhaps we're experiencing something similar?
I had to make a really conscious effort to not use my phone at times of low attention, and now actually revel in the time I get when I used to get my phone out and just browse stuff (stood in queues, while waiting for anything for any length of time, etc), and enjoy actually daydreaming or thinking about things. I find it a bit sad that this is a novelty!