I would argue 'integrates so easily into the imperative JS ecosystem' is not a differentiating factor over all the other JS frameworks, so its declarative progr

I would argue 'integrates so easily into the imperative JS ecosystem' is not a differentiating factor over all the other JS frameworks, so its declarative programming style is far more likely to be the reason it is popular (and in my experience/opinion, this is absolutely the case). If you just meant popularity vs Elm however, then sure.