Do you think the students of 2020 will be less capable, education-wise, than those of prior and subsequent years due to school shutdowns?

not much. a few months makes little difference

All the schools where I'm from are continuing but are doing home schooling, so my nephew Parker is on the computer getting lessons from his teachers through video and my brother and sister-in-law are having to spend a lot of the day with him helping him with his assignments, both in-class and homework, as well as administering quizzes and tests.  

The lessons themselves aren't as long, but he gets a lot more assignments, so parents are basically tutoring their kids in order to get them through their assignments, and generally, my brother says he or Jess sit their with him while the lessons going on because, one, they've got nothing better to do; two, they want to make sure he pays attention; and, three, they want to make sure they understand the lesson so they can answer his questions, like with math, not so much, but like with social studies, it's been a long time since they took social studies.

Basically, I don't think there'll be any difference at all.  

It depends on how long it goes on for.  A couple of months out of many years of education shouldn't make much of a difference.  But who knows really?  We play the hand we're dealt.