the Equestrian equivalent of a Mafia family ended up in a fight with a (relatively small) Hive of Changelings? Shades of Deadliest Warrior here lol

The Syndicate and the Equestrian Mafia have an understanding. Don't pry.

The changelings eat the family and take over for them.

Probably nothing relevant...

A Changeling Hive can be seen as an Military base and so fore they have recourses which the Mafia will never acquire.
So with a probability of something around 80% the Mafia would just vanish from the face of the earth.
Why?: Simple, that wouldn't be a comparison between an organization of law and order with have to follow the rules and some meta fair Crime syndicate. it would be like the Vandals versus the Slave Marked leaders and Tax-collectors in northern Africa after the Slave sellers thought it would be a good idea to try to sell Germanic Slaves to the Vandals (after they arrived in northern Africa) to make some kind of olive branch with them...
It would be more like Chickens vs hungry wolf...

Really you try to compare here two forces with each other with are SO extremely different in strength and since that you can easily say: irrelevant.

BUT: define what do you understand as a "Small" hive and the "equestrian Mafia" ?

The Smallest hive will be something around 12 Subjects, but also just because they are the first 12 Subjects. less would be probably just unable to survive. And even than this little Hive would be strong like a "Mafia" with something around 80 or 90 members and at least the biggest part of an entire big City under its "control".
And also the Mafia would here face an opponent like no other before, they would have no idea how to handle them. but also the Hive would probably try to avoid them just because there is no reason why they should ever get in some kind of conflict with each other...
Or maybe they would even become allies, the Hive needs Love the Mafia wants Money... so they can help each other... maybe... or more likely they would not have any problems with each other... they have no CPOI "Contact point of interests".

Without an CPOI they would never get in an disagreement or cooperation with each other.

So... opinions?

You're assuming the two are distinct groups. That's a dangerous assumption.