I think they precisely say the GM has that power, should she choose to use it.
Let's unpack the bit of the Basic PDF I left in the above quote, that you claim allows the player to determine the relationship.
Did you enter this service willingly? If yes, your PC has cast its fate to the whims and desires of its deity, a.k.a. the DM.
<snip>
Does your deity have a special task in mind for you? Or are you striving to prove yourself worthy of a great quest? These two go together. Yes to either gives the DM free rein to at some point have such special task or great quest arise in the game, the only difference being timing: in the first 'yes' the player's saying the task is already in place (and thus can come up soon if desired) while in the second 'yes' the player's saying she wants a lead-up story first - the striving bit - and then the quest later. In either case the ball's in the DM's court; as while a player can answer 'yes' to either of these questions she cannot then go on to specify what said task or quest might be.
This is all just begging the question. I could equally say (and do say) that in thinking about my character's relationship to his/her deity, and whether s/he has a special task in mind for my cleric,
I the player am the one who has to make all that stuff up. You are just assuming that because it invovles a deity it must involve the GM. The rules don't say that, and they don't even imply it.
And you skipped the part where the DM can have the high priest make demands upon the PC whenever he wants. There are built in obligations to the cleric class.
And
you skipped the bit that says that the cleric
might have connections to a temple whose high priest
might be in a position to demand the cleric's aid.
Here's the text again:
Most adventuring clerics maintain some connection to established temples and orders of their faiths. A temple
might ask for a cleric’s aid, or a high priest might be in a position to demand it.
Who do you think decides whether or not the cleric maintains a connection to a temple? I assume it's the player - this is all about player-established backstory. If the PC has no connection to a temple, then there is no high priest in a position to demand aid.
And even if the high priest does demand something from the cleric, that's just a social encounter. The high priest might demand it from a fighter PC just as easily!
And of course the cleric can refuse perhaps risking severe consequences for his choice or perhaps its the high priest that is in the wrong - holy cow - is that a drama bit of story i smell? Oh my - quick bring out the meta-game drama dissolver pen.
I thought you guys were talking about some stuff that was meant to be unique to the cleric, warlock and paladin - that stuff about the high priest is no different from what might happen with a fighter (captain of the guard), thief or wizard (guildmaster), barbarian (chieftain), etc.
Also, I found some interesting stuff about fighters on p 24 of the Basic PDF:
As you build your fighter, think about two related elements of your character’s background: Where did you get your combat training, and what set you apart from the mundane warriors around you? Were you particularly ruthless? Did you get extra help from a mentor, perhaps because of your exceptional dedication? What drove you to this training in the first place? A threat to your homeland, a thirst for revenge, or a need to prove yourself might all have been factors.
So presumably it's a
rule that a fighter
must have been trained. It would be a houserule in 5e to allow a self-taught fighter along the line of Percival in the film Excalibur.
You might have enjoyed formal training in a noble’s army or in a local militia. Perhaps you trained in a war academy, learning strategy, tactics, and military history. Or you might be self-taught - unpolished but well tested. Did you take up the sword as a way to escape the limits of life on a farm, or are you following a proud family tradition? Where did you acquire your weapons and armor? They might have been military issue or family heirlooms, or perhaps you scrimped and saved for years to buy them.
I'll leave it for others to resolve the "contradiction" between the paragraph that presupposes that a fighter received combat training and the one that allows for a fighter to be self-taught. But presumably this second paragraph makes it a
rule that a fighter can't have forged his/her own arms and armour - because it says they must have been
acquired! (Arguably it is also a
rule that they were either military issue, family heirlooms or bought following years of scrimping and saving - so a fighter from a wealthy family who bought his/her gear with family money would be another "house rule" - but I'll let those who know better than me how to interpret these rules sort that one out.)
And here's the final interesting bit I noticed:
[A]s fighters, they all share an unparalleled mastery with weapons and armor, and a thorough knowledge of the skills of combat. And they are well acquainted with death, both meting it out and staring it defiantly in the face.
So it seems to be against the rules for a fighter to never mete out death! This must be a "specific trumps general" exception to the rule on p 76 about "Knocking a Creature Out". (Again,
how often a fighter must mete out death I'll leave for other interpreters to resolve.)