Skyvector is for real world flight planning – SimBrief isn’t -
Never said the in simulation flight planning was useless - just if want Skyvector, Foreflight and other RL flight planning tools in sync with you in sim and simulation flight panning tools - Navigraph is a convenient way to do so. If you are happy without it, fantastic no need for the third party add-ons – they are optional
Here is a podcast with the CEO of Skyvector for your perusal -