true if that large of an increase in BTC were to happen then the BTC/XRP would go down but I don't think it would be at the same rate as BTCs rise. If you look at the "boom" back in December as BTC hit new ATH the alt market came right along with it. you could almost say it was a double whammy for those that bought in then because the BTC/XRP rose just as fast as USD/BTC so people paid more for the BTC in USD and then paid more in BTC to get the XRP. That example is probably just a once in a lifetime example of extreme FOMO maybe?
Anyways, you're right, if BTC goes up to high to fast then the BTC/Alt coin value should go down. but because the USD of most alts is determined buy Alt/BTC/USD, as BTC/USD goes up, Alt/USD via BTC would go up, just not as fast, and the longer BTC goes up the more likely it is that atl would flatten and start to go down.
this hurts my head, but is good to write down and discuss ... thank you for the feedback
RE: Bitcoin vs Altcoins?