I don’t think altcoins put much pressure on the bitcoin, but they do compete with it in some way. The main reason of the competition is innovation.
Think of it as the “search of philosopher’s stone” where blockchain is proposed as ultimate solution for any problem. Sooner or later we will accumulate enough trial and error data to contrive the basic laws of WEB 3.By this time all the “me too” coins would sink in oblivion.