Just curious, for which use cases is weight a significant problem? Even the heaviest phones - rugged or foldables - seem to hover around 300g.

That shouldn't be at all tiring unless you are holding them for literal hours nonstop, or unless you're a small child - and in both scenarios it's good to be encouraged to put the phone down after a while.

Weight is important for some people like me. I'm not anything special or have disabilities, but I really prefer lightweight smartphones. Heavier smartphones (say > 200g) significantly increases tiring on single hand use. Weight balance is also important. I'm Japanese and I can confirm some similar people exists but seems to not majority. Maybe who use smartphone in both hand never care about weight.

While reading in my bed my phone has fallen on my nose while more than once. Anyway, my usual official answer is long commute to work.