Fangio Versus the Modern Day

When asked in a recent interview whom he believes the greatest driver of all time to be, Murray Walker answered,  "Juan Manuel Fangio won five championships with four different constructors, even Michael Schumacher hasn't done that." 
I wonder whether winning with so many different constructors is really something against which the most superior driving skill and talent can be measured.  It is well documented that Fangio followed the best teams around, therefore giving him the opportunity to win so many championships. 
Fangio is described as exuding style and grace in his driving,  showing an immense amount of skill and courage, but isn't the true test of a great driver winning races in a car that isn't the best?  Maybe his real skill was an eye for spotting the best car.

Fangio driving an Alfa Romeo during the 1951 season.

He won the 1954 World Championship with points from both Maserati and Mercedes.  He made the switch because Mercedes had a superior car.  Mercedes also gave him the 1955 title.

Ferrari was the place to be in 1956.

Followed by a switch to Maserati in 1957.

He may have been considered the best driver then, but he certainly wasn't loyal.  It has been written that his strengths included being a team player and a team leader.  Obviously these were great qualities in the Argentinian as long as no one expected them to last more than a year. 

Can comparisons really be made between Fangio and modern day drivers?  There is a lot more loyalty around now.  Schumacher's loyalty to Ferrari rewarded him with five World Championships, and who is to say the same won't be true of Alonso in the near future?  Lewis has stayed true to McLaren when they haven't always been able to give him the best car.  All of these drivers have been able to show they can win races in cars that are not the most superior in the field.  Could we say the same about Fangio?