Yes and I don't even need to go further than the post above the one I'm quoting for an example of how 5e's unrestricted stacking causes the math to breakdown. That's especially noteworthy when viewed against
"The main reason to keep track of what stacks and what doesn’t stack is to keep total bonuses from getting out of hand. If a character wears a belt of giant Strength, it’s unbalancing to allow the cleric to cast bull’s strength on her as well and allow both bonuses to add up. Likewise, a character with mage armor, magic plate armor, a ring of protection, and a divine favor spell would be unbalanced if all his bonuses were cumulative. Stacking restrictions keep the game within manageable limits, while still allowing characters to benefit from multiple magic items. For instance, note that some of the items from the previous example—the magic plate armor, the ring, and the divine favor spell, for example—could work together, because they provide bonuses of different types."
With that said, context & how this tangent came up is critically relevant to the "unbalanced mess" statement. It started out because back in
760 it was erroneously stated that it was "awful"to figure out AC when some bonuses did & did not stack.
That led to 761 & 762 expressing how it was fine & not difficult because any questions of stacking were unusual edge cases that were almost always temporary & rarely able to stack.
From there in 763 someone pointed to a pathfinder PC with seven different bonuses with only one to AC & no named sources that would allow any sort of discourse. In case you lost track we were talking about the braincells involved in figuring out what 3.x
AC bonuses do & don't stack though so six of the seven are just filler.
After that things went well & truly off the rails to a couple posts of discourse over literally any cleric buff to anything that could conflict. For whatever reason that came up even though those conflicts were almost certainly deliberate for the very reason described in the DMG spoiler that referenced how it would be "unbalanced" if a cleric were unrestricted in stacking buffs+gear. In case you lost track we were talking about the braincells involved in figuring out what
AC bonuses do & don't stack though, at least the DMG specifically talked about why the cleric buffs conflict.