+1Unless you're an engineer, and spent about 3 1/2 hours sketching the design and comparing curve radii and total lengths, and both pipes are of the same length with very close average curve radii... then no. Does it matter? No.
If you split the y-pipe to make true duals, and one flowed less than the other, then you'd have uneven performance between cylinder banks. Since you're just splitting a single pipe, all your flow is going through the path of least resistance, which is usually the pipe on the driver's side. When you floor it, any backpressure created by your muffler is then bled off through the second pipe. Even if your design is completely symmetrical, you'll find when you accelerate in the cold, you'll have significantly more vapor coming out of one pipe than the other. That's the only con.