I think ECV people should absolutely not be working in schools, especially as classroom teachers.
However, I do think it's another pressure put on schools. Say it's two staff in a large secondary school, that obviously won't close the school, but it's two extra staff to provide cover for, or to get a supply teacher in when budgets for this are already being massively stretched.
Schools are really struggling with staff absence, in general. Every teacher who has a cough has to stay off until they have a test. School staff are asked to self isolate, like everyone else. Anyone who needs e.g. a routine operation which might normally only be 1-2 days off will now be off for two weeks before hand, and so on. And by asking staff to do more cover, you put them under more pressure, leading to more sickness- it's a vicious cycle.
When whole year groups are sent home, obviously it balances out, but ironically it's probably schools which are less affected in terms of student cases that are struggling the most with staff absence, as all of their classes are in school!