Bitcoin most definitely shows not only ETH but everything else out there who is king. The market dominance shown on CMC is around 68% at the moment and with so many fake trading volumes it might be impossible to ascertain the real figures but either way Bitcoin is way out in the lead.
Bitcoin is born as a Legend, more than 10 years ago, and over the past 10 years, it has shown that it is a invincible King of crypto currency market. Some years, mostly 4 years repeatedly, altcoins make their flippenings and bring the feelings that they or some of them can beat and take over bitcoin to be another King. They all failed with that and people, who have been in the market for too long enough will do recognize and remember who are always the King here.
Nevertheless, the good news for altcoin enthusiasts is good altcoins will still be there, they will not die. Good altcoins, not shit altcoins, though.