Usually when an era is dominated by one fighter that era is seen as weak. So what eras dominated by a single fighter would you term as strong? Spinks LHW reign? Ali's first reign (seeing how Liston was in it)? Robinson's WW reign (Gavilan are among many fans' top WWs)?
Saldivar's featherweight reign and comeback. Ortiz's two reigns at lightweight. Leonard and Gans at lightweight. Canto's flyweight class. Olivares' early run and first title reign. Kid Williams run to the title. Ike Williams lightweight reign. I don't think Duran gets enough credit for his lightweight run in some quarters. Dethroned a great champion in Buchanan and twice beat another great imo in De Jesus. Suzuki, Fernandez, Thompson, Viruet and Lampkin were all good challengers too. Same for Joe Brown with Charnley, Lane, Rosi, Dupas, Busso etc. Underrated if not atg comp.
For some reason lightweight seems to have the biggest abundance of golden eras that were dominated by a legend. Joe Gans, Benny Leonard, Carlos Ortiz.
Of modern times I think Tszyu would be a good claim also strictly at 140. None of the guys he beat are particularly historical but at the time the division was hot and he was dominant for so long. Gilberto Roman would be another candidate for modern times. Joe Brown is a good shout.
Usyk could fit the bill, as this era of Cruiserweights is about as deep and dangerous as the division's been.
I've always felt that the Joe Brown era which overlapped into the Carlos Ortiz era was the strongest lightweight era ever. And those two ruled. Also, I should always mention that the 1970s heavyweight era was one of the strongest, and of course, dominated by Ali.
You gotta look at the whole chess board, my man. Start at 1970 year end rankings and work your way forward. There's not too many he missed.
I'd say I've got a pretty good handle on Ali's career. Not saying that he missed anyone, but he lost to Frazier and Norton and never decisively beat Norton. And then towards the late 70's he had close fights with Young and Shavers, with many believing he lost at least one of them, and then of course lost to Leon Spinks. So all in all, I can't really say he dominated the 70's. Perhaps the first half of the decade, but seeing how close he was with both Frazier and Norton even that's debatable.