Bitcoin is the least risky investment in a high risk investment category. Its health does not depend on altcoins, but rather the health of altcoins depend on it.
This is not true and is a widely held myth amongst so called "maximalists" who tend to view the market through the arbitrary lens of a single asset - commonly known as the "monopolist" view.
Diversity in the asset class has pulled in demand out of proportion to the growth in supply or the effect of internal competition. That's not uncommon in economies.
I once lived in a street which had 1 coffee shop. the price of a cup of coffee was about the average for a residential area. Later another one appeared, then a restaurant. Over the years (about 2 decades) the number of coffee shops increased to around 30. The price of a cup of coffee is now about 50% above that in other areas. A glass of wine is about 2-3 times the price.
The influence of "competition" worked in reverse because the aggregate impact it had on "selling the street" as an attractive area to visit far outweighed the adverse effect of internal competition amongst commercial outlets trading at that site.
That's what's happening with the crypto-asset market and is also why bitcoin depends on altcoins as much as they depend on it. Without technologically superior hedges, supporting trading pairs, diversified access to the crypto-asset markets, financial specialisation and derivative platforms, bitcoin would definitely not have seen the growth it has.
Crypto is not coffee. Coffee isn't used as a currency, or for anything else other than as a beverage. Just because 1 street in 1 town saw an influx of coffee shops, it doesn't mean the phenomena can be applied on a global scale. Outside of speculation, real-world adoption is what drives crypto prices and ultimately their success. You basically just restated your assertion after giving a metaphor that doesn't apply to crypto.