The thing with tether and i guess the main reason why people have concerns about it is the fact that we can not be 100% sure anymore that every USD-T that is minted is still backed by a real USD. In 2019 they changed their official wording from "every USD-T is backed 1:1 by real USD" to "we have enough reserves to cover every USD-T that is printed and from that point on people started to raise questions. I for myself am also using more and more USDC now instead of USD-T because USDC is made by coinbase and therefore regularly audited so you can be sure that here every USDC is really backed 1:1 by a real dollar.
If Tether should really implode than i think the effects on the whole crypto market will be huge. Tether is the 3rd biggest coin in terms of market cap and if it will go down i can easily see the total market cap going down by 50% or even 75%. So let's hope that Tether will stay stable.