There is some resistance due to the oil and mechanical seal, The impeller should not "spin" like a top.... but it should not be hard to turn either,...
Really hard to confirm or deny yours is as it should be over the Internet.
Only three reasons I can think of that would be at issue.

• Damaged bearing
• Impeller seated to far into cover and rubbing the side case cover
• Impeller not seated far enough and impeller rubbing the pump cover

The impeller seated depth tolerance range is very small, only 0.27mm. If its off more then that it rubs. The impeller can be driven in 1/2 mm easily with a case cover and exposed impeller being roughly handled.

Its easy to spot though, look for a "ring" of wear in the side case cover behind the impeller and in the water pump cover.
Or better measure the installed depth of the impeller using a depth mic, or good caliper

I don't think the bearing is damaged, because there is no hard point when you hand-turn the sprocket.
for the impeller, i'm going to measure it.
In fact, i know it's not supposed to be fully free, but i found it really harder than others water pumps i use to handle.
it must eat a lot of horsepower.....

Thanks for Your answer !