this is exactly what i have been saying for about 3 years now! specially since a couple of years ago they kept saying "Tether printing is pumping bitcoin price". Tether is mainly used for altcoins not for bitcoin. of course my calculation was by summing all the BTC/Fiat currencies divided by total altcoin/Tether volume and the result was closer to 2% IIRC.
Does tether collapsing matter anymore?
that is a different matter in my opinion.
does Tether affect bitcoin price? no
does bitcoin rely on Tether? absolutely not.
does bitcoin trading rely on Tether? absolutely not.
does Tether demise affect bitcoin? most probably yes.
you see it is still a negative news and Tether won't collapse on its own, it will collapse with the company behind it and that company also controls a moderately big bitcoin exchange called bitfinex. such news can affect bitcoin negatively like any other bad news in the past.
Mt Gox collapse drove the price of bitcoin down from $1200 to $250,
it was down to $150 and it was not only because of Mt Gox. there were many reasons that caused that drop for starters the $1200 price in 2013 was a bubble similar to $20000 was a bubble in 2019 and $250 was a bubble before 2013 and $16 was a bubble in 2011 and $1 was a bubble before that. all of these cases ended with the same bubble burst and same huge drop in a rather long bear market.
there was also silkroad closure, panic sells, ASIC mining replacing GPU mining and putting a lot of hobby miners with a lot of bitcoin in their wallets out of a job, a shitton of FUD about how bitcoin is dead and is going down to $20, the start of the bitcoin civil war about scaling and ...