A fundamental assumption of administrative reformers in the late 1800s and early 1900s was that politics could only have adverse won administration. How valid is that belief? Why? How? And to what extent do current administrative structures and practices reflect that assumption? Also, discuss the contribution of various scholars to the development of public administration as a discipline.

Late 1800s administrative reforms to keep politics out of government was an important issue of the time and in many ways still has ramifications today.
Around this time, the United States was in the middle of what is referred to as the "Gilded Age" of American politics, which was characterized by major political machines and political bosses. These machines and their bosses were, in many cases, highly corrupt and perpetuated hegemony, cronyism, and nepotism. The most well-known political machine was in New York City at Tammany Hall; Boss Tweed and his "Tammany Hall Hucksters" are still notorious to this day for their level of corruption and overall underhanded approach to government.
At the federal level, before any reforms were put in place, federal government administrations, especially in the executive branch, viewed public administration in a more business-like way. When a new person came into office, it was expected that they could fill not only cabinet positions with their supporters but other positions in government as well. A major improvement in this area came about with the passing of the Pendleton Act of 1883, which put in place rules that required people going into career government positions to pass a civil service examination (or examination appropriate to their position), have a certain level of college training/a degree, and abstain from openly participating in politics.
Nowadays, we frequently hear the current presidential administration complain about career officials working in the executive branch of government who "aren't loyal." For example, consider the FBI situation that made the news last year. The president argued (and still argues) that there is a "deep state" of career government officials in the FBI who are working against the Republican agenda. In reality, the men and women of the FBI are career professionals who are just doing their jobs—that job just so happened to be investigating the president and his campaign.
Without regulations in place, a new presidential administration could not only replace all political appointees when entering office, but they could also wipe out career officials and install political supporters. Some would argue this would be a good thing: that an administration should be able to dictate their agenda and the people who execute it.
However, we must consider whether it is preferable to have political appointees that are new to the agency and government service performing the daily vital tasks within the USDA, FAA, EPA, and so on or career workers who have devoted decades to the government agency for which they work. The latter maintains stability and keeps the most qualified and dedicated workers in civil service, which in the end, is best for the organization and citizens.
https://www.britannica.com/topic/political-machine

https://www.ourdocuments.gov/doc.php?flash=false&doc=48