Hi James, I've used arcpy, arcgis API for Python, and Geopandas together and works ok once you get the hang of it. As you say, clone the arc Python environment then pip install Geopandas works fine. Here's an example of rotating something with geopandas, shapely and the API for Python.
import arcpy
from arcgis.gis import GIS
import os
import pandas as pd
import geopandas as gpd
from shapely import affinity
sdf = pd.DataFrame.spatial.from_featureclass(rotate_features_sj)
gdf = gpd.GeoDataFrame(sdf, geometry='SHAPE', crs=f"EPSG:{self.epsg_code}")
for index, row in gdf.iterrows():
rotate_pf = affinity.rotate(row['SHAPE'], row['Pivot_Rotation'], origin=(row['Pivot_Easting'], row['Pivot_Northing']))
gdf.loc[index, 'geometry'] = rotate_pf
gdf.loc[index, 'SHAPE'] = gdf.loc[index, 'geometry']
gdf = gdf.drop(columns=['geometry'])
gdf.to_file(os.path.dirname(self.final_features), layer=os.path.basename(self.final_features), driver="OpenFileGDB", crs=f"EPSG:{self.epsg_code}")