I think this happens if you simply make ArcGIS Pro Map properties to Web Mercator when publishig the layer despite data is in State Plane. So when publishing feature layer AGOL respects Pro Map document projection.
Web Mercator is not here probably the reason in performance. It is the fact that when using Esri basemaps those are in Web Meractor and if your data is in same projection it performs best as there are no data reprojections on the fly.
Our case locally is that municipalities use their data in certain Gauss Kruger zone and to get best performance in AGOL we make sure that webmap basemap is in same Gauss Kruger zone.
