As you said, it should be under Ar Tonelico series, however official categorized the nosurge series as Surge Concerto instead of Ar Tonelico series, and as of Wikipedia:
https://en.wikipedia.org/wiki/Ar_Tonelico
Instead of "Ar Tonelico" series, why not Exa Pico Universe Series as Ar Tonelico and Surge Concerto are different storylines but under the same universe?
Although it is the *prequel* of Ar Tonelico, but official didn't categorized them as Ar Tonelico series and neither Wikipedia
Also, regarding the article between Ar nosurge: Ode to an Unborn Star Deluxe and Ar Nosurge: Ode to an Unborn Star DX, I was following how steamdb title named. I understand that you used the Switch version naming and requested to delete my article, but why not doing a merger where one title redirect to another?