Whilst there are metrics out there for dead coins (no market cap or no liquidity for trading), a coin may still be alive and traded regularly, but still I don't think any alt coins should be in someone's portfolio. Alt coins are created to make the owners wealthy primarily, or become highly centralised and governed by organisations with selfish intent. The only one free of this is Bitcoin..
I don't quite agree with you here, although I was having the same thoughts that BTC is the only one that we should keep in our holding because there is almost no risk of getting scammed in this coin as we know it have potential and it can last longer and in order to save our funds for longer period of time I will definitely chose BTC over any other coin even if BTC is not going to give me high gaines while other alts will definitely do.
But still alts have there own place we should not say every alt maker or developer made an altcoin to make profit while we are also holding our funds in BTC to make profits, making profit is not a bad thing for other and good for us, its good for everyone. I hope you got my point. And secondly, there is high risk of failure of a alt token, but not every developer made an alt to make profit, many are solving real world problem, like matic, bnb and some other as they allowed integration of thousands of dapps and other relevant project onto themselves which helped many newbies to make millions.