Converting Hood under the treaty disadvantages every navy

Would a treaty requiring Hood's conversion into a carrier while allowing three Nelsons be a net gain for the Royal Navy?

No; Britain would lose the centerpiece of its global battlecruiser strategy, still need a second equivalent carrier, and provoke a capital-ship ratio that also disadvantages the United States.

Carrier conversions were still an uncertain capability, and Britain would prefer a matched pair rather than Hood alone against two Lexingtons and two Japanese ships. Adding a third Nelson changes the 16-inch balance as well, leaving each signatory with a reason to reject the bargain.