We are not far apart on paper.
The reasons why some people intentionally steer the discussion about a shot clock towards "all or nothing" approach i. e. whether it gives all answers to all questions are twofold:
1) if problems arise from its use, they will be used by the same people to claim that the new and the previous systems are both imperfect, and thus both "unfair"
2) since there cannot be a perfect solution, once exceptions are made the same people will start haggling over the amount of leeway the players are allowed.
Rest assured, those people will claim that the allowed leeway should include what is "normal" for specific players.
This is where our real positions diverge: what is reasonable to one depends on how one views the game.
As I said, it is reasonable that after a 50 shot rally there is a prolonged period of rest (and by prolonged I mean maybe 10 seconds more, not a minute). However, even Nadal cannot claim such style, so that's rather the exception.
If a player builds his style around 20 shot rallies, when the average is 5 than that is solely his problem.
The thing is, even Nadal doesn't regularly play 20 shots rallies.
His time wasting has a distinctive patterns, and here are the reasons why I think he does it:
Reason #1: Nadal forces his opponent to remain concentrated/highly alert a lot longer than usual.
If a player is waiting to receive he is highly focused, both physically and mentally. The longer the server postpones the longer the receiver has to keep this level of focus.
If that happens regularly throughout a match it literally wears the opponent down.
Same goes for the physical part as Nadal literally makes his opponents expend extra valuable energy while waiting in the receiving position.
IMO, this tactic is despicable, and should a player tries it on a club level, soon he will not find a single partner to play with.
Reason #2: throwing his opponent off: when a player is allowed to vary wildly his serving times, there is no sense of rhythm of the play.
That again delves into the concentration issues.
Sometimes Nadal makes his opponents wait above the time when they are serving! (hence sometimes it is recorded that when playing Nadal, the times of a player otherwise not known to go above the time limit, increase).
That contradicts one of the fundamental guarantees in tennis: that the players are guaranteed a pace within a certain limit.
For a sport, where the rules set how the patterns of play are learnt from a very early age and are ingrained in the player's psyche, that is a huge mental issue!
Reason #3) playing by "his" rules
Again, when you already are playing by someone else's rules you are already mentally in disadvantage
Reason #4) physical rest
Duh