Not by RAW. By RAW they are the deity's portfolio as well, and therefore RP for everyone who follows a god, cleric, acolyte or other.
Go to pages 58 and 59 in the PLayer's handbook. Tell me what Cleric Subclasses are called. Then try and tell me again what RAW says a Domain is.
You can't win when you try to refute what is clearly written by arguing that the designers are wrong with what they said.
No, I can't win when you are gleefully chortling that you "got me" and then ignoring anything that even hints that you are wrong. Making this about "winning" doesn't help either.
If you needed different domains to make different sects, then most gods would have most domains. They don't. Because Domains =/= sects. Domains are cleric subclasses. Yes, you can tie a sect to a domain, shockingly you may find that if you read about Apollo, the GOD OF THE SUN and learn that he INVENTED MEDICINE that he is associated with healing (life domain says hi) and Light (there is something called the light domain).
There was also Apollo Alexicacus, representing his role as a leader (he takes over Olympus in one mythology). That would put him in charge of civilization, that's the Order domain right? Huh, he doesn't get that.
Well,he is one of the most famous archers as Apollo Argyrotoxus, so for hunting or using a bow in war he would have War or Nature right? Oh, wait, he doesn't get that domain either.
Oh, but of course he is literally most famous for prophecy and oracles, that's why he was the patron of The Oracle at Delphi, as Apollo Manticus. That's a shoe in for the Knowledge domain, and hey, that ties into his creating the knowledge of medicine and his invention of muscial instruments. Oh wait, he doesn't get that domain either.
Death domain for his role as a speader of disease towards those he acted against? Nope. Twilight domain for his role as a protector (that's why Helm gets Twilight)? Nope.
So, we've got a sliver of what he was ACTUALLY known for, ignoring some of his most famous depictions. Sects for all of these would obviously exist. And yet, no domains. And I can keep doing this with god after god after god. Domains =/= sects. If we were limited only to the domains that are given, we'd have such a smaller and less diverse set of religions for these beings.
Not that it matters to you, you only care about "being right" by ignoring anything that challenges your preconceived notions.