There have been theories and allegations that Tether is being used to prop up the price of various cryptocurrencies. When I last kept an eye on the wild world of cryptocurrencies, Tether was at around 4 billion USD in total, and now it has grown to 19 billion, while at the same time Bitcoin is at an all time high.
As long as Tether continues to exist, any cryptocurrency USD prices should be taken with a spoonful of salt.
Because it is almost certainly being used to artificially pump the price of BTC up.
The only question is: "has the market priced this in, so the current price is a floor and we're waiting for USDT to fall away", or "has the market not priced this in and a major shock will happen when that shoe drops?"
As long as Tether continues to exist, any cryptocurrency USD prices should be taken with a spoonful of salt.