Esposito's best year came in 70-71 when there were 14 teams in the league (against the expansion Sabres the Bruins scored 36 goals in 6 games and against the Canucks they scored 35 goals in 6 games).
Looking at the league composition there were 345 skaters in the league of which 327 were Canadian born and bred players which is 94.78%.
That doesn't include a guy like Stan mikita who was Canadian bread and the early Swedish player to come to North America to play junior hockey in Juha Widing, who in 69-70 became the first mostly European trained player to have a full time contract in the NHL. In my research I also found out, sadly, that he died at age 37 of a heart attack.
Let's compare to Sakic's best season where he won the Hart in 2000-2001 when there were 884 skaters to play at least a game in the NHL of which 481 were Canadians which equates to 54.41%
Of course they were now 30 teams in the NHL in 00-01 but there were alot more players form other talent streams as well.
More importantly in 00-01 there were only 2 Canadians in the top 10 scoring that year and only 5 in the top 15.
Canada was still a great hockey nation producing as much talent, or even more than in 70-71 but obviously the claim that the concentration of talent in 70-71 wasn't that different than 00-01 doesn't hold true.
I'm pretty sure a similar trend can be found throughout Sakic's career.
Here is a list of the top scoring players in the NHL during Sakic's career
Player Season Finder | Hockey-Reference.com
Quite a different makeup from the guys on Phil's list
Player Season Finder | Hockey-Reference.com