bitcoin market cap = $8.033 billion
total crypto market cap = $8.571 billion
Bitcoin represents 94% of the crypto market cap. So, if you think bitcoin will appreciate at a faster rate on average than alt-coins in aggregate, then you should allocate less than 6% of your crypto portfolio to the alts. If you think alt-coins will eat into bitcoin's % market share, then you should allocate more than 6%. If you think you can pick a winning coin, then of the % you have decided to allocate to alts, you should invest more heavily in those you think will be "winners."
By this logic a "neutral" allocation would be 99.9% in fiat (denominated assets). By choosing bitcoin at much more than 0.1% of your assets you are already actively managing. A lot.
Also, I'm not sure whether the better measure is the eventual supply or the current circulation. That doesn't change the picture for bitcoin much (somewhat over 50% of eventual supply is already released), but definitely changes the relative position of many alts (in both directions).