Honestly stablecoins - specifically tether - is about the only thing about crypto that genuinely frightens me. Crypto rollercoaster - up down sideways and in circles - sure I'm game. Tether that is stable until it implodes...hell no. Even without direct exposure the blast radius worries me.
For what is worth, there's a huge blast radius if any of the top 3 collapse, with Tether (as the 3rd) likely having the smallest one - think of what happens to everything else when bitcoin crashes or even dips significantly.
Bitcoin's high but natural volatility is not the same thing as the price collapsing due to the system itself fundamentally breaking. For example, the Global Financial Crisis was the result of the system itself fundamentally breaking, not natural volatility, and its blast radius was immense.
Tether or other major stablecoin collapsing due to being exposed as a fraud, or a fractional reserve with no reserves, or similar, would be more analogous to the GFC. And the blast radius could be worse than any of Bitcoin's 80% drawdowns, both economically and wrt to regulatory and legal attention.