Does splitting random data reduce its security?
One way to think about this is that you are defining an encoding, and that this is just a change in representation. You are representing a 32-bit value as 3 words, and importantly this is a reversible process. Since it's a bijective mapping, there's as much entropy in the output as there is in the input.

Really, what you're doing is not fundamentally different from representing the 32-bit value in 9 base 10 digits. It's true that there is notable bias in the leading digit, but the important thing is that the full range is covered and it's invertible.