the fact is, Tether doesn't even affect bitcoin price and majority of bitcoin traders are trading bitcoin with fiat and only use Tether in their ALTCOIN trading on ALTCOIN exchanges since most of the bitcoin exchanges don't even have Tether!!!
I also think there is no
direct influence of the Tether supply on the BTC price.
However, there is some kind of correlation - in 2018 the Tether supply grew much slower than in 2017, and since the bull market started, the Tether supply growth is rising again. In my opinion, like I wrote in the other post, it's much more likely that it's simply an indicator for "interest" and "activity" in the crypto market.
We cannot also cleanly separate the Bitcoin market from the Altcoin market, as almost all altcoin exchanges (with the exception of token exchanges) are also allowing Bitcoin trading. There are even "almost-pure" Bitcoin exchanges like Kraken that use USDT.