There are a lot of variables in quick ramp-up time. For development, it depends on codebase (the more mature, bespoke, convoluted, the longer the ramp-up) and developer style (I've seen copy/paste/modify specialists ramp up very quickly, but they plateau at an intermediate level and don't have a good filter on what they choose propagate in the codebase).
Making bigger changes takes longer; taking leadership on a new top-level feature without breaking other parts of the app or distorting the architecture isn't going to happen in a few months for a codebase of any real size. The question is: is a developer who ramps up quickly going to be able to do that eventually?