I think you underestimate players. There's quite a lot a player will accept and get used to in a game, as long as there's consistency.
Is "quite a lot" a sufficent amount, if ALL players would accept a system with no money loss?
Losing a battle is frustrating to players, but that doesn't mean that all battles should now be laughably easy and impossible to lose.
Losing a battle is a part of a game which results in consequences, the player has to live with. If my party dies, i don't reach my goal, and i have to try it again. That is an integral part of every game. But if the player dies, this consequences are obvious. There is NO need, to generate additional consequences only to punish the player for his fail. To not reach the goal is already an unavoidable - and total sufficient - punishment.
There are Types of games, which makes a mechanic like this necessary ... multi-player-games. Games, were player can interact an trade with each other, need to have a so called "money sink", to limit the inflation. But in a single-Player game, there is no inflation.
A game should offer some challenge, after all, or it becomes boring. How the developer handles introducing this challenge depends on the game.
Sure. But "being punished by the game" is a very, very, very frustrating an unfair sort of a "challenge".
The key to a banking system that Jaide is looking into is that the punishment of losing gold isn't too severe and that a player would have some control. Losing money could be an extra reason to avoid death, but not something that would completely break the game.
No one, who plays a game, wanted to die. No one searches death. If the player dies, he is drawn back in the games progress and has to play things twice. If a player wants to defeat a Boss, and had to watch his "I'm big bad and evil' - speech twice, because he died the first time, I'm sure he did NOT want to die again. As designer go after your player an tell him "Look my friend, I'm very angry, if you die, an then i will punish you!" is really unnecessary, because the player himself don't want to die.
The only fair reason for a "Money loss" - or better - "a fair trade", is the offer, to let the player pay money in exchange for a restart DIRECT before the battle, in which he dies. Give the player the choice, whether he will go back to the last save game, or pay money an try the battle again immediately.
But for "go back to the last save AND give us your money" is an absurd mechanism, because it forced the player to reload. I know very well, that this is NOT exactly, what the Thread-Opener means and had in mind. But there are other Problems, because he don't uses Save-Points.
Games without Savepoints got a very big problem: Sometimes the player will simply forgot to safe. That is very stupid an silly. But it happend.
Did you really want something like this?
"You silly dumbo did not save? Bwuahahahaha! Give me ten percent of your Money, and i set you back to the last town. Or Play the last 5 Hours once again."
"But why? I had so much fun with your game!"
"Why? Because i say it! Give me money, or have once again, "fun" with may game!"
"Ok, by."
"Eh ... but ..."
*shutdown*
And there are subtle ways to encourage players to carry larger amounts at certain points. An NPC could hint at a special vendor being in the area or the vendor could have an item that teleports the player to a bank and back.
Nevertheless is the "walk to the bank" an unnecessary time-loss.
Personally, I think that we should encourage people to use different concepts and to trouble-shoot them creatively instead of just telling them to drop things because they have a
potential to be frustrating.
Oh, i never told him, that he is not allowed, to do things like this.

Besides, i never got the authority, to tell him things like this
But i think, the importance of "user-friendliness" should never be underestimated. He could do to his game, what he want. But to confuse "user-unfriendliness" with "difficulty" is not a really good way to make a game challenging
That is - at least - my opinion.