I hear you, but there's also a lot of potential for multi-domain deities.
No doubt. I am not even sure if I want the PHB to have an implied settings therefore a whole pantheon, I'd prefer a few sample deities (and more specifically I prefer generic "template" deities like "Deity of Magic", "Deity of Justice" etc. rather than named examples from a variety of settings, but I understand the latter is more popular).
My concern is to end up like in 3e where the PHB set the standard that every deity had to have quite a bunch of domains, and you ended up with two clerics of deity X that had different domains than two clerics having same domain, and then those domain spells were only 1/day/level.
I would prefer for the PHB to suggest
cohesion as the starting point, becase my rule of thumb is that it always feels better to let the DM add more flexibility later in her setting than taking it away. (So that if PHB deities all have multiple domains, and in my setting I want single-domain deities, I am sure some players will whine against me, but in the other case if PHB deities set the starting point as single-domain and you introduce multiple domains in your setting, your players are going to like you).
