I'll give you the benefit of the doubt and explain.
Usually, what Taxi's can do that uber can't is pick up riders who are hailing a cab.
That means if I'm walking down the street and see a cab, I can waive it down and it will take me to my destination.
I cannot do this with uber - the only way to get an uber car is through the app.
This is a subtle distinction but it matters and doesn't begin to get into the arrangements cabs have with hotels, airports, etc.
So what OP was saying is that if you're paying for the medallion, to recoup the cost youre incentivized to pick up normal taxi fares and not drive for uber, assuming you can generate the same value.
On the other hand you have fixed costs - you're paying for the medallion whether or not you have a fare, so you're probably better off taking the odd Uber fare when business is slow.
Grandparent is not saying that they need to get one; almost the opposite: that it does not make sense for a medallion-owning taxi driver to also drive for Lyft or Uber.
