Layout grids work well for layouts…
…but if your working with vectors and you need to align to something fast a grid is too slowso ditching rulers is not the option required here.
One of the huge advantages to figma is its intuative for work related to layout and UI…like vector drawings for layouts.
Yes I could create a layout grid but that would be slower, especially if you want a few rules/guides…and then you dont… IMHO you should be able to select and lock.