Sub-committees are informal arangements that allow committee members and non-committee members to discuss issues and come up with a proposal or set of choices that they present to the meeting. They do not require agendas or minutes as they are not empowered to make decisions.
And, yes, there are occasions when the sub-committee’s “report” is just a recommendation that the full committee then passes on the nod.
If you are concerned that the real discussions about issues in your building are being handled by the sub-committees, then rubber-stamped by the strata committee withoiut discussion, propose a motion at your next AGM that all proposals made by sub-committees to the main committee are accompanied by a written report that spells out all the options considered and why the final conclusion was reached.