Re cold - how much is due to virus changing it our body reaction changing due to immunity
In humans who have never seen RSV before, it's much deadlier than covid for the same age groups, after you've seen it and recovered though, it's "just a cold" until you're vulnerable and old enough that you've probably not seen much in recent times and then it can be the thing that finishes you off.
We obviously don't know what RSV would do to humans in their 50's,60's,70's who had never had RSV before because the test group doesn't exist, RSV has been around too long, but I don't think it's unreasonable to think it would be at least as deadly as covid when novel.
This is I assume what they mean, not covid changing