At UT I had the coolest class [and I will kick myself if I lost the notes] where we took about 30 sequential sound changes that happened on the path of Classical Latin changing into modern French. The first couple of steps took it to Vulgar Latin, which is what the Romance languages really came from, then you'd zip on through lots of changes most of the Romance languages had in common, then end up with a few that applied only to French. So far.*
Overall, Standard Italian had the fewest sound changes from Latin, but as you point out there are lots of Italian varieties and some went further, maybe in the same direction as French.
Spanish and Portuguese went off on their own path with both later getting their own groove on. But Old Spanish like El Cid had sounds in common with French or Portuguese, talking about the z, j, x, maybe not all the nasals.
We didn't do Romanian so I will never know.
The thing to remember is that the "standard" languages started as one dialect among many, and the situation in Italy or Germany where you still might find two dialects in different villages was also the norm in France and Spain. France stomped out their dialects in the 1950s. In Spain, Franco tried to with opposite results.
*Southern Spain does things similar to French such as dropping s or reducing -d- to zero. Large parts of Latin America picked up on this too. Not to say that they were influenced by French (Spaniards would be mortified) or that they'll start sounding like French, just saying there are the same processes in play. OK maybe they sound like a Frenchman from the year 800. Maybe.
To hell with this strike-through jazz