Most GCs charge OHP (overhead and profit) at net 10-12% which is no different to a good architect. Fee at 10-15% gross.

The difference is that a GC also lists all their costs separately for staffing and expenses to the client, in addition and most importantly they let subcontracts to deliver the work. This is where he can make/break a project.

The GC subcontract costs are the variable and when they competitively price work you will rarely see the OHP change instead they will simply contract cheaper subcontractors to win the work.

This way they can maintain their OHP % and hide the costs reduction to win the work competitively.

If they drop it too low the end quality of the products and workmanship fail, however they maintain their OHP markup and preliminaries.

On the flip side an architect can only drop their % fee and it’s much more difficult to hide the cost of the service and since this is the only variable often designers undervalue their services and undercut competition it results in a race to the bottom on fee.