@Vergil I didn't see Thanatos being mentioned as God-class in Volume 24, but fair enough, his performance against PDxD should put him near that. And Diehauser was also called Maou-class, not god level. He can beat non-combat gods because of Worthless, which is a huge hax advantage.
The current Maou being stronger than the first ones does not make them above the respective class. A class is not people of the same power, but of comparable power. For example, Crom Cruach is somewhat stronger than Ddraig, Albion, Azi Dahaka and Apophis, but he's still Heavenly Dragon-class as mentioned in Shin DxD 2. Another one is Fenrir who is Heavenly Dragon-class, with Typhon being comparable but Typhon is still weaker overall than Ddraig. A class is not a set level of power, but simply a range. Also, Issei didn't deal easily with Baraqiel, they were still comparable to each other and Baraqiel could hold his own.
@Burning Yeah, Ultimate-class Grim Reapers should be Maou-class on average. With Tobio in base BxB dealing with the executive without issue I would think he's at least at a Balor Rias level or such.
Truth Idea is impossible to predict, quantify or analyze, so I wouldn't use it when judging a Cao Cao matchup. Mala Ratana might work, but it's a small sphere. Could it really deal with a 360 degrees assault?