To be honest with you all and to the op as well, I personally think and believe that if bitcoin was the only crypto currency available, by now, the price of bitcoin would have been off the roof, majority of people in the world entirely might not be able to even afford 0.001 bitcoin by now due to the price, but this is actually if the market capitalization of the current crypto market in general was on bitcoin alone.
And another thing to also note is in terms of fees, by now, there would be millions, if not actually billions of transaction every seconds, and this would have caused the transaction fees on the bitcoin network to be super expensive, maybe even far more expensive than it currently is due to the current mempool congestion caused my ordinals.
Which ever way we choose to look at this, I think the existence of altcoins have done more good to bitcoin, and to investors, more than harm, without altcoins, many of us probably will not be able to transaction on the bitcoin network, expect we all switch to the unpopular bitcoin lightening network.