It is easier to notice that altcoins such as Ethereum (ETH), Cardano (ADA), Binance (BNB), Litecoin (LTC), and many others are also getting stronger along with Bitcoin.
It is true that altcoins are increasing their dominance, but if we take ETH as an example, then we can see that its greatest dominance was more than 10% higher in mid-2017 (31%), and that today it is around 19% - which means that there are a lot of new players taking part of their crypto cake. They are of course just riding on a wave created by BTC, which we have seen many times in the past.
Yes, it is obvious that the number of other crypto projects are multiplying fast. Around 2017, if I am not mistaken, there were only at least a couple of thousand altcoins listed on CMC, for example. Right now, it is numbering to around 10,000. That is quite a growth over the past few years. Of course, the majority are still shitcoins but still they are also partaking in the overall distribution of crypto funds. Many of them have also created their own communities, attracted investors and supporters, released certain products, made partnerships, etc.