I think bitcoin affects some cryptocurrency because the main market uses bitcoin. So if bitcoin goes down and ups also some crypto currencies follows bitcoin. The impact is always there. So don't worry about it because it's been nature in the crypto world.

They are not holding hands for survival, but the entire crypto market depends on bitcoin and its movement. In case bitcoin crashes, the crypto industry will disappear, but if many altcoins die or disappear will never affect bitcoin. That is the peculiarity of the cryptocurrency market.
In this market, when you are investing in many different coins will not help you reduce your risk because it all depends on bitcoin. But they can help you increase your profit if you invest in the right coin because their growth rate is not the same.

Please understand that Bitcoin is the pioneer crypto available in the market. Whatever other cryptos you are seeing today, created after bitcoin found its way to success. So it's not a matter of debate whether the altcoins follow bitcoin or not.

Personally I would say the entire altcoin market is heavily dependent of bitcoin. And very closely mimics its trajectory. But there are some obvious exceptions.  Earlier the impact was 100% but now it has reduced to some extent after the introduction of the stablecoins.

Bitcoin couldn't care less about shitcoins. Bitcoin can act on its own and simply follow its way. Shitcoins, usually go for whatever platform they are running on and follow the main project. Or at least in bigger movements, the shitcoins follows. And in turn, these main shitcoins will eventually follow Bitcoin, as it was said, Bitcoin is the pioneer and therefore, it's the drive!

OP, I get where you are heading to. I know you must be wondering why bitcoin stands to be head over other Crypto currencies in the world and why is the other Crypto market dependent on bitcoin.

At first, you should know that bitcoin is the first Crypto currency to be developed and it has no central authority over it. Hence it is a decentralized blockchain.
Bitcoin so far since inception have been termed and tagged a digital gold which no other coin has succeed to have achieved.

The maximum supply of bitcoin gives it a good spot to be in the limelight and for everyone to see.

Lastly,  the demand for bitcoin surpasses every other  coin so far and running into millions on daily basis much better that other Crypto. You could imagine if these people tell their experience on good fate about bitcoin tell me why wouldn't there be a surge in price and holders vice versa as the case maybe. All these contributes to the ups and downs of the bitcoin market which also affects other Crypto market as well.

as we know btc is the first coin and can be said to be the pioneer of all crypto, so btc is a benchmark for an altcoin if it is going to experience a price increase but it does not rule out the increase in altcoins not as fast as btc, sometimes btc undergoes corrections quickly different from altcoins which are always frequent stuck
and if btc stops then all crypto will be memory

Bitcoin is the most well-known and widely used cryptocurrency, and its price movements often have a significant impact on the prices of other cryptocurrencies. This is because many investors and traders use Bitcoin as a benchmark for the overall health of the cryptocurrency market, and also because Bitcoin is often the first point of entry for individuals who are new to cryptocurrencies.

When Bitcoin experiences a significant price increase or decrease, it can cause other cryptocurrencies to follow suit, either because investors are looking to diversify their portfolios or because they believe that the price movements of other cryptocurrencies will mirror those of Bitcoin.

However, it is important to note that not all cryptocurrencies are affected equally by Bitcoin's price movements. Some cryptocurrencies have unique features and use cases that make them less reliant on Bitcoin's performance, while others may be more closely tied to Bitcoin due to similarities in their underlying technology or market positioning.

Ultimately, while Bitcoin does have a significant impact on the broader cryptocurrency market, it is only one of many factors that can affect the prices of cryptocurrencies. Other factors, such as regulatory developments, technological advancements, and market sentiment, can also play a role in determining the performance of individual cryptocurrencies.

USDT is just a stable coin and as such you will not get the same performance as if you invested in bitcoin or ethereum, that being said the performance that you will get out of your bitcoin or ethereum investment should be similar, however while ethereum has reached new ATHs since 2017 its ATH in terms of bitcoin has never been beaten, which means that since then bitcoin has been outperforming ethereum, making bitcoin the best choice not only as an asset but as a way to make money.

Thanks for all great replies. I will check them all!