Personally, I believe that the essence of all altcoins is to create competition, or the appearance of competition, for bitcoin.
So far there is no serious competition for bitcoin thought, also many people still consider any altcoins to bitcoin as some kind of different classification. The altcoins market capitalization itself always circulating around the altcoins same goes to bitcoin market capitalization so I guess that the competition is for altcoin only.
Bitcoin is the main coin so it's not so affected by the altcoin so I agree if competition is only for altcoins.
the proof is that the value of Bitcoin greatly affects the altcoin value but not vice versa.