Is remote learning as effective/successful as being in class? How much is learning being negatively affected?

I don't believe that remote learning is anywhere near as effective ad going to class.  For one thing, it's difficult for the teacher to assist children on line as easily as in class and teachers have never been prepared to teach that way nor have kids been prepared to learn that way.  The more serious problem is that not all kids have the equipment they need to learn remotely.  If they don't have a laptop or computer at home or they don't have internet service, they are at an extreme disadvantage.  I don't know how it is in other school districts, but New York City had had a helter-skelter school schedule.  One day they're doing remote, one day they're in school and sometimes, there is not even a few hours notice when the schools close.  Parents are having to make arrangements for their kids at a moment's notice.  It can't be easy for them to just call in to work and say they aren't going to be there the moment out idiot mayor decides to close the schools.  

It depends on the student.

When you consider the fact that America's public school system now teaches to the slowest students, it is actually to the benefit of other students to learn at their own pace.  This is why private and home schooling constantly outperforms public schooling in testing.  It is also why colleges often rely on remote classes (or "labs") for certain subjects, even before COVID.  (Especially classes that are heavy math.)

And while most of the studies on how it is affecting students seem to be focusing on the negative aspects of not being around peers - I wonder if they even consider the positive aspects.  Like reduced bullying, peer pressure, and classroom distractions.

As I said, I think it comes down to the student - and their parent(s).

It is not good for the kids.  The teachers cannot do what they need to do.  The teachers are not keeping their posted schedules. Fine for older students but not for elementary.  My grandkids are back in class, it is so much better. 

For elementary online learning it needs to be setup as a one-on-one situation, or it is just a joke. 

As others have said, it really depends on the student.  With the large class sizes they used to have around here, much of a student's time was spent on their own anyway.  A teacher can only go as fast as the slowest student. 

What can be negatively affected is socialization.  Without access to other kids, they won't learn how to buy drugs, how to fold when stuffed into a garbage can, or how to be bullied.  Without being with other students, students will be forced to make "internet friends (and they aren't always what/who they claim to be).