That's a relatively good history, and raises some good points, but leaves out a few elements and gets some timing wrong.
The rise of beat journalism and "modern journalistic standards" came with the arrival of the telephone (early 1920s), and the ability for reporters to, well, phone it in. (The emergence of the telegraph and the news wire had an earlier tremendous impact, though largely on the ability for news to move between cities rapidly, if not always accurately -- I've followed some 1890s stories and noted the discrepencies ranging from misspelled names to misattributed identities: https://redd.it/39w8u4).
WNYC's On the Media covered "The History of Beats" in a segment:
http://www.wnyc.org/story/history-beatss/#transcriptContent
Beat reporting permitted these papers to develop people who had expertise. Writer Jacob Riis who's really known for his photographs was also a print reporter who made poverty on the Lower East Side his beat.... [H]e knew everything about what was going on. And so it gave authority to the newspapers. This is also important to the transition that is going on in journalism at that time. Before that journalism was an immature business. It was very partisan, often supported by political parties, and a failed politicians became editors and successful editors became politicians it was two sides of the same coin. But when newspapers established their economic independence by writing copy that people wanted to buy and if people bought a newspaper you could sell pages of advertising. In conjunction with that was enormous technological change. Paper that was strong enough to go through printing presses at incredible speeds. The telegraph delivering news from around the world. And the beat was part of that. It brought news that was reliable to the front page of the newspaper based on some form of expertise.
I'd argue that the two World Wars, particularly the second, also created the institution of the modern paper and news organisation.
Radio was starting to emerge by the 1920s, but was still pretty immature. Television wasn't a force until the 1950s, and only late within that period. Remember that the Kennedy-Nixon debates (1960) were the first time a US presidential debate was covered live. This was also the time of the first satellite links -- and they were part-time, occasional links, not part of broadcast transmission. That technology didn't mature until the late 1990s. NPR's Renee Montaigne discusses how NPR correspondents, especially overseas, would jump through hoops to get tape to the Washington studio over the course of days (and yes, physical tape), particularly from remote locations such as Africa.
As for balance and integrity, Google's Ngram Viewer is a useful tool for exploring the frequency of words and phrases in general usage. The phrase "journalistic integrity" started emerging in the 1960s, growing about fivefold through the early 2000s, at a nearly linear rate. Other related terms ("journalistic balance" and "impartial journalism") are less pronounced.
https://books.google.com/ngrams/graph?content=journalistic+i...
The terms "corporate media", "left-wing media", "liberal media", and "establishment media" appear about this time -- the first to dominate the latter, with corporate far more prominent than liberal, in Google's corpus.
https://books.google.com/ngrams/graph?content=left-wing+medi...