There's always been a bit of a tug-of-war between making a good mechanical game, and making a good storytelling environment.

If your aim is to tell stories, having consistent, intuitive worldbuilding helps a lot - it's easier to immerse yourself in a world and tell better stories in a world if the internal rules of that world make consistent sense. The further you stray from this, the more barriers you erect to storytelling.

When you get heavily into storytelling/roleplaying within a fictional world, there's always an element that involves exploring the aspects of that world and expanding its boundaries, asking questions like "what if?" - a poorly constructed world that doesn't have consistent worldbuilding will collapse if you push too hard at the edges, whereas a world with consistent rules and systems will yield new ground to explore new narratives.

If your aim is to provide a balanced mechanical gaming experience, then it's important to focus on game mechanics and balance a lot, in order to make everything fair, and to build a game that's interesting to explore from a mechanical perspective. You want your rules to exist in a state where every element has a purpose, and they work together. You want anything that costs resources or investment to yield rewards that are in proportion to the cost you put into them, so mechanical choices are interesting and result in many different approaches.

For a game like DnD, it's often the case that these two design goals are in conflict. Making an economy that's balanced around the mechanical power of different magic items results in an economy where adventurers are earning tens of thousands of gold pieces for an adventure, and regular artisans are earning one gold piece per day. If the blacksmith has an income of one gold piece per day, how can it afford to buy an unneeded item from the party for hundreds, or even thousands of gold? where did that money come from?

So the question in your design is... where is that balance point? at what point does narrative consistency have to yield to mechanical balance, and at what point does mechanical balance yield to narrative consistency? - for most designers and for most tables, this is going to be personal preference, and the answers are different. You might find if one of these two principles "feels wrong" for you, it's worth tweaking the world, or the systems or the economy to make a game that works better for your group.

I think 5e is unfortunate in that the specific systems of DnD bring these two halves of roleplaying into conflict shockingly often. A huge amount of DnD exists as vestiges and inhereted setting from older editions - to the extent where large portions of the game mechanics exist as they do because as a result of historical technical debt - there are aspects of 5e's mechanical design and worldbuilding that fail to satisfy either design principle, doing both badly because they felt they had to... (e.g. why is "Fireball" just so much mechanically stronger than all comparably levelled damage spells? That's not serving any mechanical or narrative design principle, it's just inherited from older versions.)

For something like... "the cost of plate armour" I really think WotC dropped the ball though - the reason the "mechanical design goal" and the "narrative design goal" are at odds is purely a result of the values they assigned to some items in the PHB, and those numbers propagating through the rest of the design, because mechanical purchases and treasure values have to make comparative sense.

Original core doesn't define gold values for magic items, and it doesn't provide recommended treasure packages or income curves (older editions provided these things to help DMs figure out how much treasure to give.) - the only real things that have defined gold costs are "starting gold", "living expenses" and "mundane adventuring gear"

So you could, for example, simply divide the value of every item in the "adventuring gear" table by 10, and keep the costs of living, and the incomes of NPCs the same. This wouldn't make any significant difference to gameplay - you'd just give out 10% of the money... but it'd bring the economy of adventuring more in line with the economy of the rest of the world, and allow players to operate with numbers that'd "make sense" when contextualized against the rest of the setting. In essence, it'd be a net zero mechanical change, but a significant narrative improvement.