If it were me, I would not be satisfied with that degradation. Especially if you did a full wipe and reimage from the downloadable recovery image https://support.microsoft.com/en-us/surfacerecoveryimage .
The thing that concerns me the most is
You can try recalibrating the battery - https://www.windowscentral.com/how-calibrate-battery-your-windows-10-laptop has a decent tutorial.