No it isn't. Take it from me - I have played competitive chess and have an international Elo-ranking myself. If two players ranked 1500 meet and the winner gains 12 points, then we have the following scenarios for players ranked 2890 and 2000. If 2890 wins - plus one point, he goes to 2891 (not precisely one, I rounded off). If 2000 wins, plus 23 points, he goes to 2023. As you see, winning over a higher ranked opponent is worth much more than winning over someone lower, or your own class. But winning over a lower ranked player is never completely worthless.
In theory, there is no problem calculating more results than two or three. But I don't see what winning in three sets should be worse than winning in two. In chess, there is no bonus for mating the opponent in eight moves. You get the same score if you force him into submission only after 100 moves.
Hmmmm... I may have misinterpreted the formulas. Thanks for pointing that out, I will look into it!
As for the grading of the result... In tennis, winning sets determines the result of a match, and that is also recorded in statistics, so it makes sense to include that in calculations. What my proposal is - player who wins 3 sets is awarded 1; player who wins 2 sets is awarded 2/3, or 0.666...; player who wins 1 set is awarded 1/3, or 0.333...; player who wins no sets gets 0. And that is regardless of winning a match. So, a 3:2 win would map to 1:0.666..., a 2:1 win would map to 0.666...:0.333..., 3:1 win would map to 1:0.333..., 3:0 win maps to 1:0, and 2:0 win maps to 0.666...:0. That way, a player would be awarded more points if he/she chunks more sets off of the opponent. And also, 3:0 win is worth more than 2:0, as a consequence winning a match on a Grand Slam or Davis Cup is worth more than a win on ATP/WTA series tournaments.