I think the evidence is all anecdotal about the end of Congressional earmarks. In 2008-9 Congress banned set-aside earmarks, and no one has brought that back, and there are plenty of experienced legislative people who claim that has hurt the ability to get deals done.

In addition, the fate of the "Cornhusker Kickback" is illustrative. One of the more conservative Democratic senators during the ACA negotiations was Nebraska Democrat Ben Nelson. In exchange for his vote he got Nebraska a much better deal than any other state- the Federal Government would pay 100% cost of Medicaid expansion costs, rather than 90% as with every other state. This was a classic case of negotiations and special deal cutting for important votes.

But then the news media got a hold of it, called it the "Cornhusker Kickback" and it became so unpopular that Nelson got it stripped out of the final bill. These sorts of things dying in the attention of the media mean that Nebraska got a worse deal than they could have! But it was so unpopular in Nebraska that Nelson thought it hurt his standing with the state. Which goes to the main point.

> Nebraska got a worse deal than they could have

Another way of wording that is

> the rest of the US states got a better deal than they would have

Because that extra money paid to Nebraska had to come from somewhere. And that somewhere is the people in the rest of the states.