Kevin, why do you just pick the 12 when you say that the metric is less sane than the older British "system"?
Just because 12 is divisible by some numbers. Ok. But in your "system", the 12 is not appearing very often:

5 and a half yards are 1 rod
4 rods are 1 chain
10 chains are one furlong
8 furlongs are one mile
3 miles are one league

Ok, not very much use of the 12 here in lengths, lets look for more use of the 12 in other measures.

16 ounces are one pound?
14 pounds are one stone?
20 fluid ounces are one pint?
...

So it is really very helpful that 12 is divisible by 1,2,3,4,6,12 as the 12 is used so much in your "system".

And of what help is it that the length of the measure "1 foot" is ROUGHLY the length of one foot?
If you go to the shop to buy boards for building a shelf - do you measure the board by stepping on it? Or do you let the salesperson step on the board to get its measure?
Probably you use some standardized measure stick with standard feet and inches marked on it. So the rough equivalent of length units to human body parts does not really help ...