How about this notion: There's no such thing as a "fluke" Slam. Yes, there are one-Slam wonders, but beating seven ATP players in a row--some of whom are either elite or playing in good enough form to beat elites (e.g. Anderson in 2017) to be worthy opponents--is never a fluke.
Instead there are easier or harder routes to the title. But every route is pretty damn hard, especially in the last thirty years or so. One commonality the Big Three all share is that they've had both. You don't accrue 17-19-20 Slams, or even just a few, without having some of both.
As a Federer fan I have no problem saying that he's had more easy Slams than Novak or Rafa. Scanning over my chart, Novak has probably had the hardest routes overall, then Rafa, than Roger. But they're all mixed. And you can't exactly penalize them for the easy ones, because they all had a chance of winning those Slams regardless of who they faced.
Again, take Roger. Some of his early Slams were on the easier side. Replace Gonzalez or Baghdatis with Novak or Rafa and he might lose. But similarly with his French Open finals: replace Rafa with anyone and he'd have one or two--or three or four--more. Over such long careers, "luck-of-the-draw" and easy vs. hard tends to even out.
End of discussion? Didn't think so