At least the colleges base most of the decision on 9-11th grade. DD was already accepted at her college before she had any senior grades, sports, or activities to put on the application. So, in a weird way, the seniors may be the least impacted by this.
I suspect that the test scores will help if you have them, but they will be optional this year since many haven't been able to test at this point. My DD is applying for another degree and right now the schools are saying they will accept the application without test scores but admission will be contingent on getting them (and having them at an acceptable level). She tested last year, so it's not an issue for her. And with undergrad it will be much harder since the numbers are so much greater.
I totally agree. An A at one school (or even one class within a school) does not necessarily equal an A at another. Tests are the great equalizer. As far as preparation, there is free SAT prep at Khan, which was set up to equalize things between those who had access to test prep and those who didn't. The tests help put the rest of the application in context. I've seen 4.0 HS students with a 5xx in math thinking they can be engineers, only to find out in college that they don't have the math skills to cope with the curriculum.
For kids who really don't like tests, there are test optional colleges out there and many are really good schools. They will still accept tests though.