Here are my original thoughts on the matter of OSR clerics.
In that post, I picture the cleric as an "anti-thief" without saying it clearly - and mentioned a "leader" character in the last paragraph.
Let's develop this further.
So, the thief has strong offense (many weapons, back-stab) but weak defense (light armor, low HP). The cleric is the opposite: fewer weapons, better armor, and (usually) more HP.
But that is not the only correspondence. Thieves are chaotic; clerics are lawful. The meaning of alignment changes a lot from edition to edition (see this post), so I will not dwell on that. suffice to say thieves are often depicted and more egotistical, with their own motives, while clerics are often more altruistic.
There is another important dichotomy here: thieves are lone wolves, clerics are team players.
Fighters and mages? Well, the best combination is having both of them: the fighter in the front-lines, the wizards as artillery.
But the thief-cleric dichotomy is different: thieves' abilities are GEARED TOWARDS GOING SOLO. For example,sneaking and hiding makes more sense when you're alone. Picking pockets is something you do on your own (in some games, the thief will even rob their own allies). If you fail, you fail on your own. Same for some (maybe most) small traps. And climbing.
Conversely, the cleric has abilities that HELP THE ENTIRE GROUP, and are often less useful for a single adventurer. Sure, the cleric could heal himself - if he is conscious - but cannot resurrect himself. Even turning undead is more useful when you have an ally with a bow (since the cleric cannot use one) that can shoot them from afar...
As always, this isn't clear-cut as it sounds, but it is relevant enough to mention.
So, in short, the cleric DOES have a specific role to play in the "classic four classes".
But again, as Delta says here, the armored, adventuring, miraculous
man-of-Catholic-faith is simply not a type you see very much in the
roots of the genre, if at all.
There IS a type, however, of "team-player" character we can find in the roots of the genre. I'm thinking of Aragorn and King Arthur; the type whose greatest strength isn't prowess in arms, but inspiring and helping others to achieve common goals.
Notice that these "leaders" often have powers usually attributed to the cleric - healing, inspiration, end even undead-controlling stuff.
But that is not all. The "leader" position is infinitely more versatile and useful than the cleric position. Yes, priests can be leaders - but also aristocrats, warlords, politicians, teachers, etc. Maybe the class should have some "inspire masses" power, letting the rogue keep some mountebank-like qualities? Or have rogue schemers (like Wormtongue or Littlefinger) that can influence you one-on-one, but end up exposed in front of crowds? Makes sense to me.
Of course, these "leaders" would work well in low magic settings, sword and sorcery, settings without deities or miracles, etc.
In addition, the four basic classes are a great way to classify most monsters.
The leader, especially, is an interesting type of adversary: not that dangerous by itself, but able to inspire, strengthen, organize and control weaker allies.
By the way - this is one of the things 4e got right. But that's another story.
My original post.
Delta's post about clerics.
Interesting "anti-thief" post from JB.