You are confusing the WPS requirements with the WQTR requirements. All 4.21 is trying to say is that you cannot qualify a welder out of the procedure limitations of 4.7. Use table 4.10 for determining the WQTR limitations. What the WPS tells you is that you cannot use a low-hydrogen procedure to weld with a non-low-hydrogen electrode but the welder is qualified to weld with non-low-hydrogen electrode as long as there is a valid welding procedure to follow, and the original low-hydrogen procedure is not a valid procedure to weld with non-low-hydrogen electrodes. The electrode diameter is not an essential variable for welder qualifications.