All that would do is transfer power from bureaucrats within the executive to bureaucrats within the legislature. No Congressperson is fully knowledgeable on all the areas on which they pass laws. Maybe it is a better approach than what we have today, but I'm unconvinced. At least with the system we have today, the bureaucrats are generally experts within their areas. Congressional staffers have no such experience and generally rely on lobbyists.
Think about this in good faith and try to make it work in your head, and you will see that this proposal is actually not that different from how the executive branch rule-makers work today from a day-to-day perspective, while carrying very different legal implications.
That only applies to political appointees. The rank and file are permanent employees (or were until a few weeks ago).
Anyways, not saying your idea couldn't work, only that it's not easily implemented and needs a lot of consideration to do well. It's a wholesale change to how we've governed ourselves for ~150 years. But, the idea of a permanent set of legislative experts has some appeal.