My point is that you can use your same argument against any class.
Yeah. And yet, no other class...or very few, get the blowback of the warlord. So, like I said/inferred, the warlord is doing this more than is acceptable for a lot of folks in a class-based rpg like D&D.
Why do i need to be a cleric in order to pray and make a connection with the divine? Why can't i have an assassin or illusionist that who blesses others in the name of their god?
You don't....and you certainly can, respectively. It won't do anything, mechanically, but you can certainly roleplay that.
I could just take the acolyte background, the healer feat, and moderatly armored. Those are options for any class. Praying should be RP, not mechanics.
Praying is RP. Nobody's stopping you form having your character be religious/spiritual in the game world.
Now, if you expect that praying to close bleeding wounds without bandages, hold extradimensional beings at bay, make everyone in the area "hit better"...in other words, if you want to alter reality/physical laws through the exercising of your will...that's not roleplaying. That's what magic is. There's mechanics that handle that. To have access to those mechanics, you need to be a cleric (druid/paladin/bard) or the Magic Initiate feat or some other mechanical way to adjudicate the magic. We all accept that. That is not stepping on roleplaying the character or demanding a certain roleplay of the magic-wielding class as xyz.
Why do i need to be a rogue in order to sneak and stab someone in the back?
You don't.
Why can't i have a wizard paladin who's stealthy and takes advantage of an enemy being distracted to stab him?
You can. You're just not getting the mechanical bonus of a sneak attack for that. Weapon + Str. mod from a paladin, I would think, should do just fine...possibly even with extra attacks, stab him more than once!
Sneak attack should be RP not mechanics.
That...that just doesn't make sense. Again, RPing someone taking stealthy actions (which anyone can be in 5e, just make a decent Dex. roll) does not grant the mechanic benefit that is defined as a Sneak Attack. You want your stealthy stabs to do that, be a thief...sorry, "rogue." The Sneak Attack mechanic does not detract from the ability of the player to RP a thief.
That is not the case for "what a warlord class is supposed to be." That's what I'm proposing the source of a lot of conflict is herein. Whether other classes do it to lesser extents is immaterial and reductio ad absurdum doesn't change that.
Why do i need to be a wizard in order to learn magic?
According to 5e, particularly, you don't. Any 3 y.o., apparently, interested in any area of life has a magic oozing out of their butt!
I should just be able to RP studying spell books, not have mechanics telling me how many spells i know.
You can Roleplay studying spellbooks til the cows come home. Have a great time. If you want all of the knowledge to translate into actually doing something with that knowledge/making it "work"...see above.
This is neither here nor there as far as warlords are concerned, just as a completely unrelated side note: The abbreviation of "et cetera", to say "and so forth" or "and other things"...is "ETC" or [I've only recently found out] "&c." I don't know where this "ect"...um..."stuff" began or who is teaching it. But I see it over and over by tons of posters...and almost always native-english speakers.
It's incorrect. According to multiple dictionaries, including Oxford English. "ECT", apparently, is an abbreviation for "Electro-Convulsive Thearpy." I know typos happen. I know dyslexia exists. Since it is duplicated here, I can safely assume it is neither of those. Please, people, I'm beggin' ya, stop typing "ect." Ok. Carry on. /pet peeve..like HUGE pet peeve.