BoxRec

Agreed. He fought and in a great era and was the best of that era. That says a lot.
A fighter can be the 2nd, third, fourth best fighter in one era and be better than a guy that is first in another era. Happens all the time.
When rating fighters, you have to take the good with the bad. Bad losses should be held up against a fighter. Great wins should count for a lot. You weigh them against each other when rating a fighter. In this case it clearly shows that Leonard was better than Griffith at both welter and when rating in totality without regard to a specific weight class. The film of the two confirms this. Leonard deserves to be rated as the #2 welter of all time and in the top 10 overall. Griffith was a great fighter but clearly not at that level.

I think perceptions of eras are shaped by things other than just the abilities of the fighters. One thing that stands about Leonard's time at welterweight is that the top 4 guys (Leonard, Hearns, Benitez, and Duran) all fought each other even though the fights didn't all take place at welterweight. If there is an era with a lot of talent but the fighters don't face each other due to boxing politics the era will probably not be remembered fondly by fans.

At least theoretically there is something to the notion that if in Era A the top fighters fought each other, the era would be be remembered more fondly than Era B where the fighters didn't fight each other, even if the fighters were actually better in era B

In reality it just doesn't happen. Almost all of the really, really great fighters want to fight the best available. They want to be tested. We also learn things about fighters in these fights. They are often forced to answer questions that they aren't asked against inferior competition. They often have switch to a Plan B, have to show how much heart that they have. A fighter can even get better by fighting better opponents.
Boxing politics won't get in the way of four great fighters not fighting each over a long period of time. At least some of these fights will happen.

Shame Ray had his detached retina problem. There may have been greater performances concerning Curry, McCroy, and Starling.