Again some people might take a year to make things natural
The body learns in different ways
It would take me about. 3-4 months to hit that many balls - maybe half to swing the club that much.
Pros prob do that in about 2 months
So making something feel natural could take that long so yes I don't think it is ridiculous
But he is only a pro giving his opinion - what does he know
not all pro's are the same.........and I'm only a golfer giving my opinion based on grip changes taking max 2 weeks to 'bed' in, not 10,000 balls...........but as you elude to we all take different times and learn differently.
Apologies OP for going off at tangents