You are all right but there is something that is main reason for that. All alts fallow bitcoin mainy couse economic reason. Its pure math. Let me explain
Now 90% of any altcoin volume is made in pair alt/btc and only 10% in fiat/alt.
When in 90% altcoin is traded by bitcoin than bitoin drop have to make price drop of altcoin. Why? Beacuse calculated price (btc value x altcoin value in bitcoins) is getting lower and lower beacuse btc value is getting lower. Big USD market is making it more independent from bitcoin move, becuse arbitrage bots buys cheep bitcoin, cheep alft from it and sells it on usd market. So if its big enought it can cover bitcoin drop making alt/btc price higher.
Thats why etherum is more independent. It has big fiat market with great volume. But still not high enough.
How it looks like now (90% of altcoin volume in btc pair)?
1-Bitcoin price drop.
2-calculated altcoin price $ drop
3-arbitrage bots buys altcoins for btc and sell on usd market making drop there (because its not big enought and loosing with alt/btc market) - without pushing alt/btc price higher beacuse usd market is too small to do that.
4-people seeing price drop are selling to btc and then fiat or hold bitcoin what decrise alt/btc value what even more push price lower and make more investors sell.
Thats why its so mechanical. Bitcoin drops and in the same second altcoin price drops. Bitcoin Price $ drop->Arbitrage bots->alt price $ drop->stoplos/trading bots leaves >alt/btc&$ price drop->investors sells->alt/btc&$ price drop-> next stoplos etc. thats how it looks. When it would be coues by investors decisions only ("ok ill sell becouse bitcoin - main currency- is droping") it wont be that fast i think.
Thats why when bitcoin drop 30% altcoins mostly drop 50%
It will also be possible when altcoins will have their reallife massured value. That will work like bigger usd market.
TL:DR Simply put, alt gains aren't an indication of more money moving into the market (at least right now), gains are pumped and lost because money is simply being moved around from one position to the next and not indicative of growth.
Agreed
Money are pumped into cryptocurrencies mostly by bitcoin. So if any alt drops it only changes hands (someone who has bitcoin now has alt and someone who has alt now has bitcoin - amount of fiat pumped into market is still the same). When bitcoin drops it means that someone pulled money from whole market.