"Less than a month ago, a 15-year-old student opened fire at a high school in Kentucky, leaving two students dead and 18 injured. Other incidents have been grave, but on a smaller scale."
I would like to know if "have been grave" could be replaced by "were grave". Why is the present perfect used? Because the incidents have occurred over the past few weeks, which is recent time?
Present perfect can be to talk about states resulting from past events. It probably was used because the speaker wants to emphasise that other events are still grave.
It would have been correct to use "other events were grave", with only slight change in meaning (the other events were grave in the past; they may or may not continue to be grave now)
As is often the case, the difference between present perfect and past is quite small, and either may have been used.
