Good discussion. I agree with many of the points that in some senses (not all), the "Career Slam" is overrated. But, I don't want to take anything away from Agassi (or any other career Slam winner). He did go out and achieve victory at each of the Slams, and that, in itself, is laudable, and a helluva achievement given that there really was a bigger gap in surfaces when he did it.
Who wouldn't agree that a calendar slam is much more significant than a career slam. This question comes up here and about Federer only to now switch the discussion of GOAT from # of majors won to which type of slam is better.
To win all 4 no matter the era or time frame...and just the fact that there are only now six men in history (a history that chronologically parallels most other professional sports, like say...baseball) to accomplish either feat is IMO, still a great achievement. Of course "grand slam" is cooler than "career slam" but when put it into the context of an entire career, they are both pretty cool. Laver is obviously cooler than Budge 'cause he did it twice (and I feel like if Fed was playing in the early sixties neither Laver nor Emerson would have their "calendar slams").
Any category of great achievement in any other sport where the club includes only six athletes, is an impressive club. Only 11 guys have batted over .342 for their career and this would be considered a phenomenal club in which to be included. This .342 club spans approximately the same period of time where talking about in tennis and it is almost twice the size of the "career slam" club...which you'd have to agree is not as exclusive as a club of only six.
If we narrowed the batting average club down to it's six top members we'd be leaving out guys like Williams, Gehrig and Ruth...that's a pretty exclusive club. Now, if you said, who hit over .342 for their career AND also won Triple Crowns, then the group gets more exclusive and prestigious, just like its does from Career Slam to Grand Slam(6 member down to 2)...but to be in the group of six career slam guys is still a really cool thing...just like it is still pretty stinking cool to have batted over .342 for your career.
Comparing eras is a silly prospect no matter what the sport. It's like putting a 350 lb current-day defensive lineman against a 225 lb offensive lineman from the '50s (or even the '70s). The tennis athlete and equipment has evolved to the point that #50 in the world right now would put a regular thumping on Tilden, Perry, Budge, Kramer, Gonzalez, or Rosewall. But, I think Federer is the only guy you could put a wood racket in his hand and his game would immediately translate to the long era of guys from Tilden to McEnroe. Rafa would have to totally relearn how to swing with a Chemold Elite in his hand...it would be miss-hit city.
Anyways, I'm getting off subject, but...what other variable are you gonna use to compare the "most complete players" from different eras other than how they competed on, and won championships on all surfaces.
Let say we're gonna try to figure out GOAT. One way is to start with the club for only guys who've won 10 or more majors. That club only consists of 6 guys: Tilden, Laver, Bjorg, Emerson, Sampras and Federer. Now how are you gonna narrow that down but to add the filter of greatest number of surfaces on which slams were won...now we are down to Laver, Emerson, and Federer... the only to have won more than 10 and on all surfaces. Now you have to decide what is more important...total number of slams won relative to if a "calendar slam" is better than a "career slam" (taking into account here my opinion that those guys wouldn't have their grand slams if Fed played with them. Sampras is NOT EVEN in this debate when structured this way. OR you could go by total number of slams won as your first variable (which is how it seems to be done lately)...two guys at 14...now how else are you gonna narrow it down but to add the filter of number of surfaces won on...now we are down to Fed.
IMO it comes down between Federer, Laver and Emerson because of all the variables and filters I spoke about above (and I haven't even applied his 20 straight major semi-finals). Either way you boil it down, Federer is the only guy in BOTH conversations and for that reason I'd fill him in as the GOAT...with pencil. When he get's his 15th slam I'll feel confident enough to write him in with pen.