This is barely related but I bet that the extra 70 mb of ram isn't even waste - it's probably an optimization. Its possible they're spinning up a JS VM preemptively so when you do navigate you have a hot interpreter for the inevitable script. Maybe they allocate memory for the DOM too.

Probably the case, I felt bad using this as an example as I don't know the specifics, but thought it is an easy way to convey my point (sorry if so Brave developers).