Yes, well put. I like your point about titles, because winning one has a lot to do with who the competition is. As we all know, there are some "one-Slam wonders" who were inferior players to some who didn't win Slams. Players like Davydenko, Ferrer, Rios, Mecir etc were better than T Johansson, Gaudio, etc. Or we could look at specific years, like 1998. Rios was ranked #2 but didn't win a Slam, but did win the Grand Slam Cup, three Masters, and seven titles overall. Sampras was #1 and won a single Slam, but otherwise was inferior, winning no other big titles and only four titles overall. The other Slam winners--Rafter, Moya, Korda--all had lesser seasons to Rios.
This is also why I think any conversation about GOAT cannot stop at Slam count but has to at least take into account rankings. I'm even fine with stopping there as rankings take into account all performance.
Those five ranking ranges also constitute "tiers" of players. A "second tier" player spends most or much of his prime in the top 10, might slip into the top 20 at times or sneak into the top 5, but his prime level is top 10. Tsonga, Berdych, Ferrer, Nishikori, Thiem, etc. Of course any system of categorization (like tiers) is only ever about 80% accurate; there are always borderline players that are hard to categorize. Wawrinka is a great example: he was arguably the second most dangerous player on tour from 2014-16 but never ranked higher than #3 and finished all three years #4.