Alright, here is a reason why players don't like other players making insane amounts of credits: the economy and price balancing in game.
With new ships and even the fleet carrier set to come out soon. And the average wallet of players going up and up because of get rich quick exploits (which is what they are, not intended, not taken into account when designing the game) the prices of those new assets will align with the average of all players, not just the ones playing the game as intended. So multi billion price tags may pop up for stuff like motherships. Making it unattainable by anyone but thee hardcorest of players and the crazy rich people who broke the economy and caused those prices to begin with.
So yeah it might be hypothetical but it's not based on unreasonable asumptions.
Making money in the game has never been easier (not counting exploits obviously) and it gets easier with every patch, yet people keep complaining that they can't upgrade ships every two mission. What would be the point ? The pace of progression has already been strongly undermined. Back when the game came out, your first million was a great achievement. Now it's just a small stepping stone towards the Anaconda bought in less than a week of regular play.
First off, it is not an exploit because it uses game mechanics that are commonly available, even if the outcome is unintended. An exploit produces an unfair advantage, and this was available to everyone.
In regard to it breaking the game, the economy has been broken from initial release. Your argument is founded in leveling logic, but the game doesn't use leveling to manage the content. As a result, you have Mostly Harmless AI running around in Anacondas. A player just coming into the game takes one look at that and thinks, I should be able to do that. When they figure out that the AI doesn't follow "the rules" in ship generation, the player goes looking to balance the situation.
The fact of the matter is that Elite: Dangerous uses a hash of gaming techniques in an attempt to control "progress" without following the development strategies those control methods are made for. Risk/reward doesn't exist in the game because the pay is dependent on your rank with the faction. Cash gates are in place, but the AI doesn't "level" with you, meaning that the gate doesn't offer a sense of achievement, only a sense of restriction. The "rank" locked ships are effectively cosmetic because they are not superior to normally available ships and the pirate AI gets them regularly. I could go on, but the I believe point is well established.
Added to all of that is the fact that many players don't engage in continuous money flow mechanics, explorers being the primary example. Once you get the ship you need to do what you want, you stop playing the money making game because you have literally left the economy for extended periods of time. To those players, the money needed to do what they enjoy is nothing more than a large gate.
One of the great stories from Distant Worlds 3302 was the Sidewinder that made it to Beagle Point before Engineering. That was done through the massive efforts of the community, otherwise it would not have been possible. Now, stop and think about that not as an incredible story in cooperation and determination, but in terms of technical capability. A starting player couldn't have done it, even with Jump Boosters, because the drive isn't capable. To that theoretical player, DW 3302 was an unavailable option.
Money is more than just a score.