Economically, it's much better to have the stock exchange versus a farm. Before it was a question of percentages, basically it was a question of whether or not the added population of a farm compared to the existing population would be more than however many percent that your econ building gives. Basically you end up with planets with 3-4 farms, and as many econ buildings as you can fit on the planet after the necessary morale buildings.
Now though, the income is a square root of the population. For those who fear math, here's an example you don't need a calculator for: Square root of 25 is 5, square root of 36 is 6. Basically, if you manage to get 9 more people you would only get 1 more credit. To get one more credit, you need to get 13 more people for a total of 49. This is probably one of the worse forms of diminishing returns in existance. Because of this, realistically you would NEVER want to use a farm, it's just not efficient to do so. The ONLY case where it would be beneficial to do so, would be if you had one of those +300% farm tiles on a large world.
Now, having said that, it's still better to have at least 1 farm on most of your worlds 7 size and above purely for the population and it's benefits to influence and defense. It also gives you a reserve to draw from for troops to invade people. So, now that we have established that most worlds will have 13 billion people (5 from initial colony, 8 from intensive farm), there is absolutely no reason to put one more farm on there. More farms = more morale buildings because of lower base morale, and the returns would be much less than before. Instead, you could fill all those slots with econ buildings for a much more benefit.
The result? The current taxation system have basically turned the large econ world formula from 3-4 farms, 6-8 morale buildings, the rest econ buildings, into 1 farm, 2 morale building, the rest econ building. This is the most beneficial in terms of the amount of money this world will make. As a side effect of this, it is so much easier to keep people happy, you can tax 69% without much worry. So grabbing a morale resource or two and you're completely set to conquer the galaxy.
In conclusion:
Does it make sense? no, certainly not to me. My first thought was that the people are evading taxes and are hard to catch on high population worlds. Of course, I'm immediately reminded by the game summary that SAYS the people listed on a world is the people who pay taxes. The only thing that I can think of to explain this is that the planetary government is taking basically all of the money from you (so they can build roads and homes or w/e for all those people, I guess).
Do I like it? no, before, making econ world was a skill in balancing farms, morale, and economic buildings. Even though I definitely knew a formula, there was still always adjustments that needs to be done everytime population reaches a new level. Now, I just put them all down, in order, like a planetary queue at the moment I colonize the planet. I NEVER have to look at it again, unless I have a ton of extra cash (that it probably made for me) to go in and buy it a ton of upgrades. Some might argue that this is a good thing, and I won't disagree, but it does make the whole "design and build your planet" part of the game way too simple for my taste.
Can I deal with it? Oh yeah, hell, I even told you guys how to make a ton of cash really fast in this post alone. The point is not that making money is harder, it just changes how you go about making money. It's a switch away from farms and morale buildings to more economic buildings. I don't really mind less influence, I'm getting annoyed that I keep conquering everyone culturally without an influence starbase anyways (which might actually be a good thing).
What else? This is just a beta, Brad already mentioned that he's already planning alternative methods to handle this because he doesn't really like it very much either in one of the journal replies. Having said this, I don't think we need to complain much more. Right now, it's a beta, I already told you how to make a ton of money if you still choose to play it as it is. IMO, it's not THAT big of a problem. However, if it seems so to you, then simply revert your game to pre-beta and wait for the full version. You did make a back-up right?