The reduced reputation requirements are to bootstrap the site during the private beta. They return to normal when the site opens to the public.
problem with [everyone] having the ability to close questions…
That's not true. Closing a question still take a consensus of five people to close a post. And so does re-opening a question if we get it wrong.
Less participation during the private beta?
Your suggestion to slow things down and limit access to the editorial tools used to build this site misses the point of a fast-paced, closed, private beta. Before opening a new restaurant, you typically invite 40 to 80 of your closest colleagues to a closed, invitation-only event to try out the menu, work out the kinks, give the place a bit of a lived-in look, and to give your founding staff bit of experience (reputation) to get them off to a running start in preparation for opening day.
there are relatively few active members and many "silent" members
I'm not ceding that ⤴ point, but if that's true, I would call that a failed private beta — or at least the folks who signed up explicitly for this event are gravely misunderstanding why we are here.
That's how sites get closed.
You are a founding members of a new community. A private beta is (primarily) a site-building exercise to establish what types of questions work (and don't work) here. But that needs more participation — not less — to try new things and fail quickly by closing (and reopening) those experiments that just don't work.
The worst thing to happen to new sites is when initial efforts take off in a bad direction… only to be met with apathy or a diminished ability to oppose or try something better, setting a more sustainable course for the site.
That means a lot of participation — to fail quickly and try again — and that means more participation, not less.