Duel = a type of fight
Dual = double
You have a lot of “I think” in your posts. Every poster responding has said the same thing: no, you don’t.
It is not that common that every poster on a thread has the same response. Your challenge is to figure out if the posters know more than you do. Having been on CC for a fair few years now, I can tell you that @blossom, @eyemgh, and @Mwfan1921 are long time, experienced and knowledgable posters (@SouthYankie is new to me, but the posts are on point and beautifully succinct). They are adults who have seen many admissions cycles, talked to many AOs, and shepherded kids through admissions across multiple schools.These are not HS students guessing or trying to figure this out,
It is your GC who will answer the rigor’ question, not what your friends do. If you are concerned, ask your GC if your planned curriculum will meet the "most rigorous’ standard. If so, you are good to go.
As for whether to take a class junior or senior year, here are couple pros/cons either way:
Junior year: the work load typically gets heavier and the material harder, and Junior year grades carry the most weight. In addition, many people start getting heavier leadership roles in their ECS as juniors, putting more pressure on your time. If your DE classes are at the local university (not in your HS classroom*), there is also travel time to consider. Finally, sometimes students so overload Junior year that their senior year options are less rigorous, so might look as though you have chosen to take an easier senior year. There are colleges that specifically look at the senior year courseload to see that the rigor is the same or higher. So, in the context of those factors: does putting Data Structures in Junior look like a good plan?
Senior year: EC leadership roles can require even more time, and the general advice is to consider college applications (including researching, writing essays, getting all of the LoRs in, gathering all the financial information if applying for financial aid, completing the forms, etc) as a ‘class’ in itself. Unless you have an early acceptance, first semester grades are critical. If the goal is to demonstrate interest and commitment, having the class on your senior year transcript checks that box.
*note whether the DE is in your HS or at the college can affect whether colleges will accept the credits