You are right that it seems that other coins have the potential for greater than 10x ROI, but you need to consider that all money going into crypto starts with bitcoin, a beginner first hears about bitcoin and goes and buys bitcoin, then he might hear about altcoins and invest parts of his bitcoin investment into alts. This means that bitcoin is the MOTHER of all cryptos. If today you buy 1 bitcoin, it will not turn into 2 as you said, (It's not magic)
You will always have 1 bitcoin but it's price will increase. And this increase in price as the late majority and mass adopters hear about bitcoin will be exponential.