you have already answered your own question!

there can be a new coin some day that takes bitcoin's place but so far we have seen thousands of new coins and none of them were even good let alone want to come close to bitcoin to take its place

No one knows. Better alternatives can come, but I really don't see a better coin coming any time soon. Most likely not even in our lifetime in my opinion. Bitcoin is simply just too far ahead in terms of everything.

As long as there's a single GPU or ASIC that's mining blocks, bitcoin will still work.

One of the weirdest questions I've ever heard. Did you see the bitcoin dominance rate? It currently represents more than 60% of the market.

I do think that Libra might serve as a good opposition when it comes to cryptocurrency world.
As far as right now is concerned, we know that there is not even a single coin that is near the place or price of Bitcoins , when we talk about cryptocurrencies , people tends to naturally think that we are talking about the Bitcoins.
This is really something that has been not a matter of one day but it's been due to the highs and lows that it has gone through since 2009 and the recognition it received.
Some coins come and go , sometimes they increase in price for some time but that's it for them.
I don't think anyone will take place of Bitcoins.

I don't know about this because the changes happened so fast, but my assumption that Bitcoin is still able to maintain its position to be the king of crypto. Even in the past 5 years, there is still no one who can take the place of bitcoin, including ethereum, which has a high popularity, but still can't afford it.

Yes, you have answered your own question that bitcoin will always be the king of the crypto market and no one will replace it.
although Libra is rumored to be competing with bitcoin but it's still too early and in my opinion it won't happen.

Bitcoin has been and will continue on being  the reigning king of the crypto for a long time, not just in terms of its high price that just keeps on getting up and up, but also in terms of trading volume, and to be honest that is really hard to beat, but who know maybe the facebook Librea will have a huge success and people all over the internet will start using for various thing, and it might just might be able to compete with bitcoin in terms of trading volume and not in terms of price because that is impossible to do.

Most altcoins that offer faster and cheaper transactions can do so because there is no demand for their block space. If 99% of your block space is not being used, sure, your transactions will be confirmed quickly. I do however have to point out that fast and cheap transactions don't mean they are safe. Most altcoin chains can easily be rolled back, attacked, etc.

People need to understand that most altcoins are being donated value and liquidity because they are paired against Bitcoin. Without Bitcoin the majority of the altcoins wouldn't exist, and those that would exist would trade for pennies. With governments cracking down on non compliant exchanges altcoins will be under fire even more, especially the more exotic ones.

In the end, with Lightning there is no reason to complain about 'slow' and expensive transactions anymore. Try it out and see for yourself.

Current BTC Dominance is 62.4% and it took 10 years for it to climb this far and to be called the king of crypto.
However, I believe in change and innovation, so it is possible that a new coin can pop up in the future (maybe 10 years from now) and share the BTC dominance, maybe 50/50 or 51/49.

But still I'm skeptical in considering any new coin to become king by replacing BTC.

There is no need to bother yourself on whether Bitcoin will still remain the king of the crypto market because Bitcoin is and will always be the king of the entire crypto ecosystem. Bitcoin was introduced in the world alongside blockchain technology, and blockchain technology is currently taking over the entire world. There is no blockchain without the mention of Bitcoin.