No, it couldn't. They said "no base class" not "no NEW base class". The 3 new jobs literally don't have a class. It's the job, period, with the requirement to get them being to be level 50, clear the ARR story, get into Ishgard, and get them quests. It doesn't matter if you're a level 50 DRG with nothing else, you could open up those 3 new jobs.
The class > job system is bad, no matter how you look at it. The 2 jobs from one class concept is even worse, and brings way too many problems. With SMN and SCH, the problem is different roles. But if they shared the same role, the problem would then become, are these really different enough to merit a second job? For example, they would have easily made THF and NIN come out of ROG, and give THF a different style (maybe make it a trap job?), but since they didn't, one has to assume they either aren't smart enough to have thought of it, or they thought it wouldn't be different enough to be worth it.