Welcome to the site !!
So you verified the de-compressor was working while kicking it over and it engaged , but it was still hard to kick ?? , if with the plug in , the kicking is a little harder then i would guess its working as it should , if its real hard to kick , then its not working , I find it hard to kick over any 4 stroke with Tennis Shoes , it usually hurts the arch of my foot without some kind of arch support in the shoe/boot (normal shoes not MX boots) if i kick more than just a few times , it did it when my bike had 11-1 compression and it does it about the same with 12.5-1 compression , not really much difference in kick feel , with the de-compressor not working , its like kicking over a old Harley , it will kick back if you don't give a full hard kick , so i am thinking it is working
Take a large rubber band and bind the de-compressor so it won't move (wrap it a few times so its really keeping it from working) , then kick it and see if its worse , it should be , this will determine if the de-compressor is actually working or not
Don't forget there is a timing alignment mark on the clutch side as well , under the big round plug to the rear of the water pump