IIRC, Merckx raced in the 60s and 70s.
Merckx raced 13 WC RR, these are the winner nations:
Belgium - 5
Netherlands - 2
Italy - 4
Germany - 1
UK - 1
These are startlists from every WC RR Merckx won.
Competing teams and riders for World Championships ME - Road Race 1967. Top competitors are , and .
www.procyclingstats.com
Competing teams and riders for World Championships ME - Road Race 1971. Top competitors are , and .
www.procyclingstats.com
Competing teams and riders for World Championships ME - Road Race 1974. Top competitors are , and .
www.procyclingstats.com
I'm not putting startlists from other years but as you can see, Belgium was heavily favored to win WC. Less nations and Belgium had clearly more riders than a lot of other nations.
You can't run away from this.
IMO PCS is a reliable source but if someone knows these startlists are incorrect, please tell me, I don't want to have an opinion based on incorrect facts.