[Part 1] Okay, so it turns out that Delta From The Eminence in Shadow turned out to be FAR stronger and skilled than I first thought. After doing more study in the LN's, and seeing a bit of the Seven Shadow Chronicles (which are the only parts of the MoG Games that are canon), it would appear that she's pretty much a walking titan.
First of all, during the early days of SG (recently before the Templars/Priestess Victoria Arc), Shadow instructed Delta on a technique which allowed her to maximize her magical power, and she somehow managed to effortlessly imitate it... which even Beta had trouble doing.
More so, it turns out that according to Shadow and Lambda, Delta is the single most talented, skilled, and fastest of the 7 Shadows ("Skilled" I find contradictory due to her intelligence. By the time of Volume 5 Zeta is the fastest as Shadow said she had gotten stronger than before and Zeta managed to blitz and outrun her)
Not only that, it is also stated by Alpha herself that Delta (still around 10 btw) had surpassed her power the rest of the Seven Shadows in terms of power by far... in turn meaning that she would be superior to an Overdrive Shadow in terms of power (Shadow would still destroy her in a fight, objectively; no need to explain or even assume) as Alpha before even being cured was said to have more magic power than Shadow himself; this most certainly would have changed by the time of Volume 5 due to Shadow's Mana Conservation ability.
NGL, looking back on Delta's fight with Zeta, it was mainly Delta who caused a lot of the damage to the environment, and even managed to level and entire forest within minutes.
Furthermore, Shadow posing as "John Smith" stated that he most likely could never defeat her using threads alone, and that her senses and reactions surpassed his considerably. To be clear, characters like Alpha, Shadow, (and arguably Zeta) are still superior, but only due to higher skill and magic control... TEIS really has flipped the switch.
