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But I think bitcoin have its own advantage compare to altcoins. Bitcoin is the first cryptocurrency and it become one of the superiority value among all coins including altcoin. Also in my opinion, the volatility of bitcoin is as much as the altcoins, because it is so usual in the market that the price of altcoins is following the price of bitcoin. If the price of bitcoin is increasing, alts will follow it and the market will start to bullish.
if we compare clearly I agree with what you said that bitcoin has the advantage of all existing altcoins, because it can also be seen that the movement of altcoins all depends on what bitcoin is doing, whether it goes down or up. when bitcoin is experiencing a deep correction then all altcoins also experience it, which indicates that is the influence of bitcoin.
but it's not that there aren't any good altcoins, there are still a lot of good altcoins that can be seen from the ranking on coinmarketcap/coingecko because the market cap is also pretty good.
so it's not wrong if you can't invest in bitcoin, you can change to a good altcoin, by analyzing it first.