You could use a box of crayons… or leggos (sp?) to demo that… and the demo wouldn’t run like you think it would. You have to have a “source” of diversity…LOTS of diversity.
That requires sheer numbers in the population… so if you want to have fewer years of mutations… then you have to have a MASSIVE population for longer than expected… not a SMALLER population.
They’ve done estimates of world populations for the last 5000 years… and they’ve projected back from there…
this would be like trying to hide 600,000 men in the Sinai Exodus… it’s hard to hide those kind of numbers!.. since you would need to have MILLIONS of extra humans to generate the alleles we have today.