I will admit, I do not know a whole lot about complete immersion in a completely online format as an instructor. As a student, I have had a lot of experience.
Before my current teaching position, I worked for a publishing company in the Digital Installation dept., as part of the National Geographic team. It was an area for all digital based products from kinder all the way to college level. My dept was focused K-12 products. There were many products available in reading, grammar, and science, but none for math. Occasionally, when I was out of things to do, I helped the other teams catch up, so I got a glimpse of the higher education academia realm. These were the areas where international accounts were.
In my area, I did have contact with districts that conducted education wholly online. It appeared that it would usually be a sub-district within a district. I internally made the vague assumption (not saying it was correct or not) that these types of schools were designed for kids who have problems adjusting to traditional school. It also appeared that some states used virtual learning more than others and especially where it is year round school. I had also given product training to a teacher who was a solely virtual schooling teacher,
What I think about virtual schooling is this. I believe it hugely beneficial for advanced kids so they aren't being held back by the other students. I also believe it beneficial for students who have social issues that interfere with learning, There is an awful lot of time being wasted doing "housekeeping" in a classroom such as paperwork, lunch count, homework procedures, journalism, and the most time consuming of all, behavior problems. I must spend at least an hour a day dealing with the same behavior problems daily. These problems are expected due to some very traumatic backgrounds.
How I know how much time is wasted is how I compare it to a brief homeschooling. While my son is very outgoing, my daughter is the opposite and struggles socially. I kept her out for about a month until we moved. I made lesson plans to be accessed online with instructions under the guidance of her grandparents with explicit instructions. I would then check it in the evening, She completed all her work in 2 hours. 2 hours!! I gave her way more than I would my own students (she was the same age). After this little experiment, I noted that her writing and spelling greatly improved. This leads me to think about how much instructional time is really wasted in a traditional classroom. There are many facets to homeschooling and virtual schooling and I am not asserting it should be one way or another, but I do believe a combination allows for students to progress at an an individualized rate.
Now, I use a whole curriculum program for my students. I have one who can do crazy mental math. He took his placement test and he has advanced 2.5 grade levels in just 6 months. When I do math lessons, this is what he does because he is bored. He is also ELL so it is hard for him to explain his thinking to other students in a way they understand.