Today, many altcoins have surpassed or nearing their ATH vs BTC valuation. More notable coins are nearing their ATH in USD valuation.
Well, sorry but what are you talking about? Can you give me that examples from let's say TOP50 coinmarketcap list without tokens like BNB?
A few notable ones (that's not BNB and that have been around since at least 2017 - first half of 2018, experiencing the major BTC decline), coins like LINK, ENJIN, Raven, LTC and many others in the top 100. Other coins like Waves have come close to their BTC valuations (around 50% of it), while Bitcoin is still valued around 25% from it's ATH (we're in an intermediary period, since there was major market movements, so i can't comment on that atm, some alts will correct accordingly to adjust).
The entire point here is that some altcoin's dominance continues to grow on Bitcoin, essentially divergence as time progresses forward. When coins reach close to their BTC valuations, and lets say people predict Bitcoin will reclaim grounds of 10k.. 15k..100k and etc, those specific altcoins have matured over BTC and will be worth (in USD and BTC) their most ever. Coins can hit ATH in USD, strictly because they are paired or valued on Bitcoin's price (for the most part, CMC). It's more rare that coins hit ATH vs BTC, while reflecting valuations lower than their ATH vs USD. It's even more rare to see both come together, in the case of Raven, ENJIN and BNB soon. So, if Bitcoin continues to increase to 10k, these altcoins will his ATH at every moment in time
I'll reserve my opinions on BNB, but if you're playing closer attention to the market, it actually has decreased inversely to BTC valuation over the past 7days.
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Shift in topic / off-topic ----
Ultimately, why is BTC vs altcoin valuations important? Because, everything in crypto is directly paired or linked with Bitcoin in one shape or form, from exchanges and etc. There has been tendency to move away from this, by pairing ETH and other alts. The more significant movements is pairing with stablecoins, which further reflects on divergence away from a crypto-crypto centered market dominated by only Bitcoin.
For the most part though, the majority of alts still behave and will continue to correlated according to Bitcoin's price movements. There are many more outliers today and the outliers will continue to increase with time, as the markets diverge away from being dominated solely by Bitcoin's movements. It's not uncommon for random altcoins to diverge and go on a pump-spree, this was pretty common even 4 years ago, but all-in-all, it's not uncommon for some altcoin bullish movements to pave the way for many more altcoin movements.
The graphic below depicts Bitcoin dominance. Ofc it's because there are more and more altcoins per day, but some altcoins are also overtaking and growing against Bitcoin's dominance. Again this is due to a surge of new valued coins, but Bitcoin is losing ground due to 1000 cuts. We did see Bitcoin dominance shrink to like 43-44% in 2017, Bitcoin recovered to 55% total dominance (during mid-winter), but that's again shrinking indicating a bull-market (imo) is occurring (we saw it happen in 2017), starting or truly about to begin (that doesn't mean that we are not going to potentially see losses again btw).
I can get more into this, there's ofc some nuances and arguments against what was stated, i know many of those arguments already. I did shift the topic here quite a bit, and went into some discussions about Bitcoin's dominance. There's no denying the trend for altcoins is in-fact, changing (growing) and that's because of money, legitimacy and infrastructure.