> Was Roman wine better than pre-Roman wine in that region?

Not necessarily better, but they made much more of it. https://en.wikipedia.org/wiki/Ancient_Rome_and_wine:

“Ancient Rome played a pivotal role in the history of wine. The earliest influences on the viticulture of the Italian Peninsula can be traced to ancient Greeks and the Etruscans. The rise of the Roman Empire saw both technological advances in and burgeoning awareness of winemaking, which spread to all parts of the empire. Rome's influence has had a profound effect on the histories of today's major winemaking regions in France, Germany, Italy, Portugal and Spain.

The Roman belief that wine was a daily necessity made the drink "democratic" and ubiquitous; in various qualities, it was available to slaves, peasants and aristocrats, men and women alike. To ensure the steady supply of wine to Roman soldiers and colonists, viticulture and wine production spread to every part of the empire. The economic opportunities presented by trading in wine drew merchants to do business with tribes native to Gaul and Germania, bringing Roman influences to these regions even before the arrival of the Roman military. Evidence of this trade and the far-reaching ancient wine economy is most often found through amphorae – ceramic jars used to store and transport wine and other commodities.

[…]

Among the lasting legacies of the ancient Roman empire were the viticultural foundations laid by the Romans in lands that would become world-renowned wine regions. Through trade, military campaigns and settlements, Romans brought with them a taste for wine and the impetus to plant vines. Trade was the first and farthest-reaching arm of their influence, and Roman wine merchants were eager to trade with enemy and ally alike—from the Carthaginians and peoples of southern Spain to the Celtic tribes in Gaul and Germanic tribes of the Rhine and Danube.

During the Gallic Wars, when Julius Caesar brought his troops to Cabyllona in 59 BC, he found two Roman wine merchants already established in business trading with the local tribes. In places like Bordeaux, Mainz, Trier and Colchester where Roman garrisons were established, vineyards were planted to supply local need and limit the cost of long-distance trading. Roman settlements were founded and populated by retired soldiers with knowledge of Roman viticulture from their families and life before the military; vineyards were planted in their new homelands. While it is possible that the Romans imported grapevines from Italy and Greece, there is sufficient evidence to suggest that they cultivated native vines that may be the ancestors of the grapes grown in those provinces today”