Eh, it probably buffers against overreaction, especially when a correction in fundamentals is being mixed with a reaction to new pressure.

But this is still a good point: if the market really is overheated then short-term monetary policy won't change that, and we can expect a lasting hit regardless of how disease issues play out. And it's not necessarily going to be obvious what's market movement and what's disease-related; I wouldn't be surprised if some over-hyped companies seize this as a chance to lower guidance faster than they normally could without spooking investors.