from the past until now bitcoin has remained and will always dominate compared to altcoins, and there is no need to doubt. without bitcoin, altcoin can't do anything. And many investors and traders trust bitcoin more than altcoin, because bitcoin is clearly more promising.
Altcoin would not exist if there is no bitcoin, that's the right way to describe it.
They are just alternative for the original currency which is bitcoin, and it's the king now, it's obvious, alts are just following it's movement.
Last year was the latest example, bitcoin did not move a lot, then altcoins slowly dumping and some loss 90% of its value in its ATH prices.