Okay, Terri, let's back up here a little bit.
Some comments are made ascribing section 3.7.3.2 and areas of Table 3.7 which will not apply because you are not dealing with fillet welds. So let's make sure we use the correct text, Tables, and Figures to see what the code says about your situation.
When your filler is a Group II and the base material is included in both groups we need to stick with the Group II portion of the chart as this is the common denominator for the work being done. The only difference here really is that the Group II's are Low Hydrogen and thus reduce hydrogen levels which means you can then utilize lower preheats and optional welding parameters not available with Group I materials and electrodes. All Group I materials can be welded with electrodes included in Group II. And remember, this is only a matter of PreQualified Groupings of Base Metal to Filler Metal. You can do any combination if you want to get a PQR and then establish your WPS's off of the approved by testing report.
Now, you said the face opening is 7/16-1/2" which is only relevant when making sure of one's depth to width ratio. This is not going to be an issue with material 1/2" thick and welding from both sides with the groove joint you have specified.
Next, from your description it sounds as though the backgouging did not get all the way to clean material and/or was not properly cleaned if an air-arc was used by grinding for proper weld preparation after air arc.
So, with all the information currently available my personal choice (notice 'personal') would be to base the Pre-Qualified WPS on a three pass weld, maybe four. A root from the first side with one or two more for fill and cap from that side. Then, backgouge and run one pass on the other side to fill it up. This is going to make a good clean weld with limited heat input and lower chances for slag inclusions when trying to run FCAW too thick and trapping slag under molten weld metal. Trying to run few passes by going slow and thick with FCAW small diameter electrodes is a mistake. Then, if the backgouge had to go really deep because of low penetration in the root then trying to get into the root while carrying enough metal in the molten pool is not easy. More passes with better control reduces the chances of lack of fusion, slag inclusions, and other discontinuities which can result from these conditions.
The welder is to use the supplied WPS for his guideline for the job regardless of his personal opinions. If the boss wants it done a certain way, then he just supplies the WPS that way within the manufactures specs on electrodes and the restrictions from the applicable code and that is how it gets done. You don't always need the code to tell you exactly how to do it. The codes leave certain items to fabricator specific applications, processes, choices, and best practices.
Total time on job because of acceptance vs rejection criteria and actual finished product per customer specifications is the factor that counts for profitability. If the boss has it bid a certain way and his way works and makes money then that is what should be done.
We hear it all the time: 'There's more than one right way to do a job!' Yes there is. But, often most of the ways have already been tried and this is what works best for us. It is within the code parameters and it gets the job done with minimal repairs, total time, and thus makes money. I have let the hired help try it 'their' way. Then, I show them how my way is faster and thus more profitable. The customer isn't paying for the employees ego. They are paying for the boss's reputation, knowledge, and experience. IF you can prove there is a better, more consistent, more profitable way, then I'll listen and we will have other employees try it. See, just because ONE person can do it doesn't mean everyone can. The shop method must be the one that will work everytime for everyone. If there is only one person it doesn't work for, they get removed from the equation. It isn't the procedure at that point, it is the person. Either they don't want to do it that way or they can't do it that way but when the majority can then we don't change procedure we change personnel.
He Is In Control, Have a Great Day, Brent