I think scratching the religious/philosophical underpinnings of any of the D&D settings/multi-universe would reveal problems that do not hold up well to any time of scrutiny, but I'm not sure if that is what the OP is asking. Any of the numerous discussions/arguments on I certainly don't have a problem with Dragonlance's Cataclysm; or at least no more than of the other D&D moral semi-religious ethos. It has a real worldish, slightly Old Testamentish vibe that sets a nice backdrop for the world. The people became corrupt, pulled the world out of Balance, and the so-called 'gods' of the setting sent down a fiery mountain to adjust and punish them, thereby creating the setting for the story.
From what I gather of the OP, they think that was a very jerkish move on the part of Paladine et. al to pull, causing all that suffering and destruction. Especially for a so-called 'Lawful Good' type. It basically boils down to a variation of the age old philosophical argument/question of "Why does God allow bad things to happen to good people?" Which religion has been dealing with, in one form or another, for ages. There's a guy over here named Job that really went the rounds on that one. Basically, it boils down to the fact that God, or 'gods' see much more and further than mortals do, this mortal life is not really the some total of existence for us. There is more beyond, which is something we have to accept on, well, faith.
As far as the Wall of the Faithless in FR, I really can't say, as the underpinnings of that campaign setting never really interested me that much.
I have a problem with this line of thought, especially in the context of DnD.
DnD is a game, and I as the DM have to know the answers to the big questions of the setting. If there is a reason for something, I need to be the person who knows the reason.
"No one is allowed into the Catcombs beneath the castle" is something I can tell my players, and they don't have to know why, they can just assume it is for good reason. But, as the DM, I need to know why. Because some NPCs need to know why. If there is a Demon Lord in those Catacombs, then I need to know it exists, or I can't run the game properly. And if it is sealed, I need to know how to break that seal, because that is a goal of some of the antagonists.
So, as the DM, if I have the Wall of the Faithless.... I need to know why it exists. Because saying that the "gods see much more than I do" when I determine what those gods see in the first place, is nonsense.
And, if a player came to me after their character found out about the wall, and asked me if there was a reason for it, and my answer was "No, it is only there to make the Faithless suffer for their lack of worship" then that player suddenly has a problem. Their cleric, who might be kind and merciful, now either much reject the gods who approve of such torture, or come to the conclusion that people who commit a high enough crime, like being Apostates, deserve torturous punishment.
Either way, this could ruin a character. And sure, maybe the character could just take it on faith, but the player now knows that their character is deluding themselves. Which is also a problem.
So, the solution would be to not tell the players, but then... what is the point of a setting element that no one ever sees, hears about, or interacts with.
And, this isn't a case where a canonical answer does not exist, one does exist. The gods want to make the Faithless suffer for their lack of worship. That is the reason, canonically, that the wall exists.
