Well, it depends. We have social and competitive dancers on the forum, so answers for various questions here are different for these groups. In my opinion, we should divide what is needed for dance to work "good enough", which is essential for social dancing, from what is needed to satisfy the judges on a competition, meaning your dance should also be a nice representative of a particular genre and interesting to watch
To me, there are skillsets needed in partner dancing that are basic
foundations, regardless of whether the goal is to please the partner
(socially) or the judge/audience (competitively). Good dancing is
good dancing. The proof of the pudding in the eating is in the implicit
"ratings" dancers give each other.
One of the primary differences between partner dancing and other
types of dancing is the ability to "work off each other's bodies."
This is done thorough connection. Even if the lead+follow is
reduced (through routines for instance), connection is still key,
as it determines how partners interact with each other (fluidity,
timing, cohesiveness, etc.).
Your assumption that social dancing only needs to be "good enough"
while competitive dancing has some "better" facet is just
a bias that has little to do with lack of connection in Samba, socially
or competitively. Unless people have decided Ballroom Samba is
just a line dance.
In case of competitive dance, it can work perfectly well for you and your dance partner, but it doesn't mean it will actually look as expected by adjudicators, as many things won't "just happen" the way they like them. So you can dance on latin competition for instance cha cha in salsa style, with bent legs etc, but even if you have better body movement and connection than other couples, you won't see the final. That's how it is
Even if you have "perfect" (to judges, whatever that is) leg movement,
you may not get into finals (because of bad connection, bad costumes,
whatever), because judges are fickle. It's the politics of dancing.