The real question is always where the cutoff is. You can't compare with Fangio and Clark and nor can you compare Fangio to Clark. You can't compare Hamilton's time now to Prost's time then but can you compare Hamilton's time now to, say... Schumacher's time then?
It's probably best to stick to major technical changes to be reasonably fair.
1950-1958 - the front-engined era
1959-1970 - the wingless mid-engined era
1971-1976 - the aero development era
1977-1986 - the first turbo era
1987-1993 - the mechanical development era
1994-2005 - the hunt for NA power era
2006-2013 - the V8 era
2014-2021 - the hybrid era
Of course they all overlap slightly but quite noticably no driver has extended huge success from one era to another. Or perhaps more importantly, no team has. In the '60s Lotus generally had the fastest cars and Clark made the most out of them, although he also lost a lot of races and probably two championships to the notorious unreliability. In the early '70s Tyrrell got it right with Stewart taking two championships and Cevert being set for more if it wasn't for his untimely death. From there on it was a really mixed bag all the way to the late '80s when McLaren swept the floor with everybody else - until it was Williams' time until the mid-'90s. After that Ferrari got their act together and Schumacher ruled the circus, the V8 engines again shuffled the pack and this time Red Bull nailed it with Vettel going on a spree. In the beginning of the hybrid era Mercedes was the only one to hit the mark properly and Hamilton has used it to his great advantage ever since.
Which leads me to the question, how can we ever compare drivers properly, even inside the same era as the cars are so different? Probably the only way to do it is the comparison to their team mates (and again their team mates) and it can lead to interesting results.
Let's take Vettel as the first example.
In his first full year in 2008 he was paired with Sébastien Bourdais, a four time CART champion. Vettel took the points 35-4. After that he beat Mark Webber five years in a row, lost once to Daniel Ricciardo, and again beat Kimi Räikkönen four years in a row before losing once to Charles Leclerc. With Ricciardo being one of the fastest drivers on the grid, having himself gone 1-1 against Jean-Éric Vergne who is now a two-time Formula E world champion and beating Max Verstappen in 2017, Räikkönen being one of the few who was able to outdrive Schumacher in Ferrari's heyday, and Leclerc perhaps the outright fastest guy of today, he's done pretty well.
And of course Hamilton.
In his first full year in 2007 he struck it even with Fernando Alonso, steamrolled Heikki Kovalainen the next two years, went against Jenson Button for a total 2-1 result over the next three years, against Nico Rosberg for a 3-1 over the next four years, and then beat Valtteri Bottas three years in a row. Alonso is hard to judge truly properly thanks to his politics in every team he's been in but he's unquestionably very quick, and Button and Rosberg are both world champions themselves, although someone might say that Button only because of the Brawn loophole car. However, Barrichello - himself far from a slouch - couldn't get enough out of the BGP 001 to beat Vettel that year.
Pretty much all the rest of the quick ones have been mentioned in those two paragraphs. It's hard to say which one of them is really the king of the 2010s because they haven't really been in comparable cars but both have beaten very impressive drivers, and also got beaten themselves by a couple of surprises. Perhaps the real conclusion is that Button, Ricciardo and Rosberg are all much better than they've ever been given credit for.
The odd comparisons could go on much further. Take Kovalainen for example - a Race of Champions winner, neck to neck with Rosberg in GP2, faster than Alonso in Renault's testing before his first season, took pole in Silverstone 2008 for McLaren in pretty much the only race where he wasn't driving a fuel tanker in qualifying on "an alternative strategy". In reality it's all down to circumstances, which car suits who better, and as much as people hate to admit it, who is favoured by the team.
Yes, I'm a bit bored sitting at work when just about all the customers are on summer vacation.
