It is not even clear it's "good news", it doesn't "still mean" at all, read carefully under "Edit 2" of my parent post. It can also mean that it will take longer. R0 must be reevaluated, and threshold is f(R0). We don't even know the "correct" function for the threshold, even less which people contribute in which way. We don't know how much were infected up to now, the high numbers weren't random samples, prevalence in global population is much lower than in a few hot spots where a lot of deaths happened. "Math is hard." Immunology is complex.

The maths you refer to do not make that judgment at all. They indicate that, assuming all the assumptions that go into those models are true (they aren't), herd immunity may be lowered, but not by much.