The fact is that ALTs rise faster than bitcoin when market is bullish and fall faster when the market is bearish. For good balanced portfolio you shoul also buy etherium and bitcoin.
Maybe this is your wrong statement, although you see that the altcoin speed increases but you do not calculate the value of any higher coin. As for BTC you see that they only increase 1-2% but in value they will increase extremely high, referring to the money they probably raised to $ 500-1000, the other altcoin is not able to reach this price.