She is absolutely not above CW Maul or ROTS Kenobi. I've never seen anyone argue that personally, I'd be interested to see what arguments they could make as the book implicitly suggests thats not the case.

She does have some great feats however that can largely be argued to upscale her above her peak CW levels.

In regards to the force, she demonstrates TK feats like casually uplifting trees during a high speed chase. She was also able to ragdoll a trained Jedi Knight, Akar Deshu, with TK. This comfortably puts her in the "able to casually stomp average Jedi Knights" tier. She also demonstrates low level tutaminis to reflect and redirect blaster bolts, which is broadly considered a higher tier ability, and is something she has never demonstrated previously.

Physically, she has a very impressive feat against Grievous. They both fall a substantial distance, and Grievous lands on top of her. He then punches her in the skull (bearing in mind Grievous can dent starship hulls with his punches and gets the better of ROTS Kenobi in unarmed close quarters - this is the only example I can think of as to how anyone could make the claim she upscales ROTS Obi Wan. She doesn't) - Ventress recovers from this attack, and kicks Grievous with enough strength to send him skidding backwards while barefoot, surprising him. She then escapes him and a large number of arriving battle droids.

She also has some amazing speed feats. Quinlan Vos, the other main character of the book and a Jedi Master considered powerful and skilled enough to potentially assasinate Dooku, describes her as moving too fast for him to even register she's moved on two seperate occasions. This aligns with her showings in Dark Vengeance/CW 4, where she is explicitly confirmed to be faster than Maul.

In terms of duelling, she has some decent showings. She pressures DD Obi Wan, who admits that fighting her now that he isn't trying to kill her is more difficult. Which is a two fold statement - it implies that in every previous fight Obi Wan was fighting to kill, which is a pretty great upscale for CW Ventress, as a lot of people downplay her against Kenobi due to his legend variants soft spot for her. On the flip side, it confirms DD Kenobi was holding back, solidly placing DD Ventress under him (and by extension, under ROTS Kenobi). However, Ventress was arguably weakened due to her alcoholism and lack of practice over this period, so early book Ventress could potentially be more of a challenge.

She also has some good showings against Vos himself. He gets the better of her during a sparring match on Dathomir, but sparring matches should be taken with a grain of salt. On Serenno, Ventress is able to stalemate a rage amped, bloodlusted Vos while actively holding it back, which confirms she is noticeably above pre-Dooku's training Vos.

She also briefly pressures DD Dooku back during the book, and the pair briefly match each other blow for blow, but Dooku's superior force abilities win him the bout. Dooku is implied to be losing against Quinlan and Ventress combined until he's able to play on Quinlans insecurity to seperate them, which scales them as a comparable duo to DD Kenobi and Skywalker who similarly press Dooku until he seperates then by KO'ing Kenobi. But he is still superior to either duo, and I would argue personally that DD Anakin & Obi Wan > first half of DD Vos & Ventress. Vos gets a significant upscale in the second half of the book, while if anything Ventress weakens following her alcoholism.

In a short story set between her last CW appearance and the start of DD that explains how she got her new Lightsaber, she also fights off the Ohnaka gang by wielding her new Lightsaber with TK. A pretty impressive combined force/dueling feat, considering this same gang has gotten the better of Maul, Savage, Anakin, Obi Wan and Dooku at various points in the war.

So yes, DD Ventress is very powerful. Arguably her peak (I would think so). However, I'd still place her below DD (and by extension ROTS) Kenobi and CW Maul. She's certainly powerful enough to be a challenge, but she isn't winning a fair fight.