Nice job -- I have examples using statsmodels for similar (not time series) data [1,2]. I typically use this for EDA before regression modelling, so dependencies in that scenario are not a big deal. But I might weep if someone told me no scipy in production.

[1] https://github.com/apwheele/Blog_Code/tree/master/Python/Smo...

[2] https://andrewpwheeler.com/2020/09/20/making-smoothed-scatte...