Whatever the performance of BTC in the market also altcoins are affected.
Yes, bitcoin remains number one and it is perhaps more of the reason why newbies are advised to invest in it should they be confused with which cryptocurrency to invest in. Bitcoin because of it's status remains the most reliable when long term is considered.
This is because 99.99% of the human beings involved in crypto start by purchasing bitcoin in exchange for fiat and then exchanging the bitcoin for an altcoin.
I take it that it is an assumed statistical figure that you have put forward, because 99.99% is too much. If you actually ask people to know, some people first purchased Ethereum because they felt that they had already missed out on bitcoins, a lot of persons had that same feeling of missing out, the percentage of these people has to be greater than the remaining 0.01% left from the assumed 99.99%.