I think the risk is that these are derivative instruments which depend on a strong BTS, aren't they?

So logic would imply that if a large amount of the increase in BTS price and all the bitFiats created was due to excess funds from the rest of the crypto world pouring in, then that means that when liquidity is drawn out it would also disrupt the bitEconomy heavily if it too was pumped with inflated Tether-priced assets. I think there is still tremendous risk even in the assets you listed, even if I personally agree that they are safer than Tethers, I do not believe they are invincible.