OP. There is plenty of ways to make gil right now even if you don't craft or gather. Just from running a few dungeons at level 60 you'll be getting tens of thousands of gil. If running content like that constantly to make money isn't enough for you, go out and kill enemies for loot drops. Still pure combat without being a gatherer or crafter, and some of the more expensive materials on the MB are ones you get from killing annoying monsters over and over again for material drops. Or if all else fails, go run FATEs constantly for hours on end. You get a nice bit of gil from them to begin with, and all the Grand Company Seals that you get as well can be traded for items that can be sold on the MB for a decent price. Or if THAT'S not good enough for you, farm tomestones and use those to buy the rare materials from the vendors. I know that before the Relics came out I was nearly capped on Law so I blew what I had on a material that I sold on the MB for about 300k if I recall correctly. OR IF THAT FAILS, start a sell party for EX primals. While I don't support sell parties in the least, that is still yet another way that you could make gil without crafting or gathering. OR IF THAT ISN'T GOOD ENOUGH FOR YOU, then you can always just farm EX Primals for materials. King Mog's Whiskers are selling for about three million right now on my server, (and selling fairly quickly), which is more than I make from gathering normally in a few weeks unless I'm making an actual effort to make gil. Then there's also the option to simply use your Ventures wisely and level your two free retainers that you have access to to level 60 and let them gather items to sell. Just off of my main retainer I make about 10-20k a day from doing one 18h venture, and she's an Arcanist not a gatherer....
You're complaining that it's nearly impossible for pure combat players to make a decent amount of gil, but I just listed eight very viable methods for making money in game that doesn't require a crafter or gatherer class at all. Yea, you won't be making money as quickly as a dedicated crafter or gatherer, but what would be the point of even playing as those classes to begin with if they didn't allow for making money at a faster rate or saving you from spending money?
From reading a few of the other comments in this thread, as well as a few of your own, it becomes readily apparent that you're not complaining about the cost of materia as much as you're complaining that people who diversify how they play the game have more options than people who only play one part of the game. There are benefits to focusing only on combat of course, such as, (hopefully), improving your skills in general allowing you to preform better in content when compared to players who haven't practiced as much, or the fact that you'll be more familiar with enemy patterns. It's only fair that the people who craft or gather likewise have their own benefits in the form of more gil and easier access to crafting and gathering items. What's more is that it's not like these people have put any less time into the game than you have. In fact, most people who have the same level of equipment as you do, but who also have at least one crafting or gathering class leveled, have put more time into the game than you have......
EDIT: I guess part of my point is that the OP's reasoning and claims even on the first page alone are insulting in many regards. As is, even if you don't actively try to make money from crafting or gathering items for profit, it's stupidly easy to make gil in this game. I know that on an average night of just doing roulettes or leveling dungeon runs, I walk away with about 50k from a few hours worth of runs, before we even begin to count in anything I make from my retainers selling stuff or their ventures.....