Could Ranger and Wasp have been traded for another Yorktown?

If the United States had not built Ranger and Wasp, could it have built another Yorktown-class carrier instead?

Yes; their combined standard displacement was more than enough for another Yorktown-class carrier on a simple tonnage comparison.

Ranger and Wasp displaced roughly 14,800 and 14,900 tons standard, while the Yorktown class displaced about 20,000 tons. On that simple treaty-tonnage basis, omitting the two smaller carriers would have left enough allowance for another Yorktown-class ship. This is a comparison of standard displacement, with Hornet used as the example of the larger carrier that could have been built.