I know most people think of molecules, atoms, nucleus, neutrons, quarks, leptons, etc., are all precisely the same across all similar items. But they are not.
Two hydrogen atoms are completely unique to one another but it is harder to measure the differences than larger items because of the difference in scale and since they both generally behave the same way no on cares to explore their uniqueness until the difference is noticeable and worth exploration.
We know this to be true because nothing can be perfectly split and if nothing can be perfectly split then there cannot be two particles that are exactly the same. If a single particle cannot be split into two equal particles, then no two combination of particles can produce the same unique item again. Therefore, all particles must be truly and absolutely unique in some fashion.
So, the idea that contrary leptons can be symmetric is absurd.