Not much influence will occur, altcoins are only complementary, let alone altcoins that do not have good credibility and development, which only tend to take advantage at the beginning of some investors who enter and then leave the altcoin.
Many new altcoins become trash and die. So that altcoins will not have a big impact on bitcoin.
But conversely, Bitcoin will have a huge impact on all Altcoins if the bitcoin price is unstable.
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But if you think about it, if there were no altcoins, BTC would have more adoption because any person who wants to buy crypto would buy BTC, but many people are buying altcoins because they want returns very fast. I feel this is the only way to put it: altcoins somehow divides the industry and if it wasn't that way, more people would have probably invested in BTC, and the price may be higher than what it is now.
The people who bought altcoins when the hype was early, were expecting huge returns with the pumping boom that was about to happen.
It has been a common practice since the ICO era, I even participated in several presale altcoin projects which provided quite large profits,
maybe 100x of the capital I used or even more.
Bitcoin comes first, if altcoins are less then bitcoin is always an option, Altcoins are just as complementary.