Oh, you’re right, and when you’re right, you’re right, and you, you’re always right!
Well … it doesn’t matter if you properly use 24-bit dithering to create 24-bit mix. With 24 bits you have so much headroom (approx 20dB more than human hearing range), that even multiple generations of dithered audio doesn’t generate audible dithering noise. Just be sure, you don’t select 16-bit dithering algorithm on your dithering plug-in, when creating 24-bit audio file.