You mentioned four names, strewn about five centuries. Five Years in 19th century europe did see more (durable) output by historians.

The qunatity of historians and the reach of their published work in the 19th century had another quality.

Not yet.

The Hun is always either at your throat or at your feet. Winston Churchill

...do you really want to claim our perception of the roman empire is more influenced by Livy than say Gibbons?

Perhaps by Livy through Gibbons.

"It is not necessary to have hope in order to persevere."

All died before 1800. David Hume wrote a History of England, Voltaire best known history was The Age of Louis XIV, but also wrote The Age of Louis XV, The Chronicles of the Empire from Charlemagne to Ferdinand II in two volumes, a two volume history of Russia under Peter the Great, etc. The American historian of the enlightenment Peter Gay had high praise for Voltaire as a historian, as did my French History Professor. Gay from wiki:

Yale professor Peter Gay says Voltaire wrote "very good history," citing his "scrupulous concern for truths," "careful sifting of evidence," "intelligent selection of what is important," "keen sense of drama," and "grasp of the fact that a whole civilization is a unit of study."

Just previous in the same wiki article there is this:

Voltaire had an enormous influence on the development of historiography through his demonstration of fresh new ways to look at the past. His best-known histories are The Age of Louis XIV (1751), and "Essay on the Customs and the Spirit of the Nations" (1756). He broke from the tradition of narrating diplomatic and military events, and emphasized customs, social history and achievements in the arts and sciences. The "Essay on Customs" traced the progress of world civilization in a universal context, thereby rejecting both nationalism and the traditional Christian frame of reference. Influenced by Bossuet's Discourse on the Universal History (1682), he was the first scholar to make a serious attempt to write the history of the world, eliminating theological frameworks, and emphasizing economics, culture and political history. He treated Europe as a whole, rather than a collection of nations. He was the first to emphasize the debt of medieval culture to Arab civilization, but otherwise was weak on the Middle Ages. Although he repeatedly warned against political bias on the part of the historian, he did not miss many opportunities to expose the intolerance and frauds of the church over the ages. Voltaire advised scholars that anything contradicting the normal course of nature was not to be believed. Although he found evil in the historical record, he fervently believed reason and educating the illiterate masses would lead to progress.

....

Voltaire's histories imposed the values of the Enlightenment on the past, but he helped free historiography from antiquarianism, Eurocentrism, religious intolerance and a concentration on great men, diplomacy, and warfare

In many ways  Leopold von Ranke narrow focus on politics and diplomacy was a big step backwards from Voltaire, as was the rise of nationalist 'national histories' in the 19th Century. Voltaire was likely by far the best historian working prior to 1800.

But I agree with your point as to the change in the nature of writing history, the number of historians, etc. that characterized the 19th Century, as I noted in an earlier comment.

"It is not necessary to have hope in order to persevere."