a common concern i’ve heard is that we’re storing the data twice, in the Log and in the View(s), so it’s inefficient and duplicating and why not just have one database for everything

Btw, someone making this complaint needs to learn more about how databases work. Databases need to arrange data so it is easily readable. There are many approaches to this but just because you have "one database" does not mean that database doesn't internally save the data twice, in some way or another.