Venice can easily get cities with MoVs. On top of that, they are fully developed cities and you get a lot of units as a bonus. So if you never anger the AI, you can just keep sending your trade routes to civs with highest culture output and eventually win the game with tourism. Taking out a single civ with a high culture output at the end may help, but for the majority of the game it's best to just stay in good relations with everyone.
MoVs aren't free, city-states are terrible at developing their cities, and city-states are usually spread out making them impossible to defend.
On the other hand you just let your neighbor expand straight into you, you can pick off his cities, puppet them and have a somewhat more compact empire.
You're of course welcome to play the game however you want, but a lot of people would disagree with the fact that Venice is meant to be played in permanent peace.