If it works as intended, it is not a bug. You don't have to like it.
It's not working as intended, as that would require an indication thereof. There's no indication whatsoever that this is some kind of intent, and it makes little sense when - as indicated above - literally EVERY OTHER of the 5 don't work this way.
The tooltip text is: "Increases a world's gross Income." For both MarketCenter and ShoppingCenter.
The fact that the market center has synergy with entertainment buildings, which are tied directly to taxes (so yes, money) makes the adjacency make sense to me. It is designed with a bit more subtlety than a straight-up percentage bonus.
And again this is NOT indicated anywhere. It's just what you infer based on the adjacencies they've given it. Which is why the current setup is a BUG.
(edit) in fact, when they took the wealth adjacency off the market center, they changed the Colonial Bank from 1/civ to 1/planet. This more than makes up for it.
No, it doesn't. Colonial Banks are decidedly inferior to what the prior Wealth Adjacency Market Center was. A nice little 3-triangle of Market Centers (with +1 Adjacency) has +6 Adjacency. The same triangle with a Colonial Bank has but +4 Adjacency as it stands now. And the Colonial Bank itself is the same power as a Market Center, and inferior to a Shopping Center. It gets much worse with 4 or more adjacencies. Not to mention that the Colonial Bank is the 5th Wealth tech, and obtainable about the time planets are full built out, so counting on the CB as some sort of compensation for the brokenness that is the MC/SC is just incorrect.
So why the super-special "it's not a bug" treatment for the two introductory Wealth Buildings? When everything else doesn't do that. Why not use (again, like EVERYTHING ELSE) auxiliary wealth buildings for differentiation? Wealth is one of the 4 core stats in the game (Manufacturing, Research, and Morale being the others). It's not anymore different or important or special than those other 3. So why on earth treat it differently.
That people can play around it or adapt their playstyle does not in any way diminish that IT IS A BUG.
As to the +5 Raw.
Name me any way to get +5 raw production, with ZERO moral effects, on any world that isn't incredibly fortunate enough to be surrounded by a massive asteroid field, or which is either your homeworld or a Precursor Factory World that you've built several Approval buildings on. Now, name me any way to do this within the first 50 turns. Now name me a way which you can instant-buy that, for barely more than the cost of 1 introductory building.
A +5 raw boost is massively overpowered, even in late-game, but especially when you can literally buy it right about turn 30, and easily triple the entire output of a planet at that point.
It's even worse on smaller maps, where, due to limits on the total number of planets, you're not going to get more than a half-dozen all game, and won't have more than 3 total when RG-278 is a viable purchase.
In Crusade-based games, with very limited ability to gain raw production through ANY means, +5 is a massive bonus.
And again, it's something that is completely out-of-balance with all other Mercenaries.