Front derailleur hard to move due to gear cable angle
Having looked through the manual it seems that your shifter cable emerges from the frame on the right hand side of the bike, so the converter should be installed with the pin to the left, which should result in an acceptable angle between the shifter cable and derailleur lever.

I'd definitely rule out all other possibilities that might result in excessive effort required at the shift lever. Detach the cable from the derailleur, put some tension on it (may need to grip it with pliers), actuate the shifter and make sure the cable runs freely. Check the cable run from the shifter to the derailleur make sure there are no snags, housing is properly inserted into stops on the frame etc. You may even want to remove the cable and clean and lube it.

I'd also check the derailleur adjustment. especially alignment. You say the chain rubs at the back end of the cage - if the back end of the derailleur cage is toed out sightly it may be causing the rub. Park Tool has a great step-step video on front derailleur adjustment that can be found here: https://www.parktool.com/blog/repair-help/front-derailleur-adjustment