General meh to generic plot powers completely not dealt with in game, and completely indicative of powers. If a Level 1500 Overlord can do all those things...why would she really have that many issues taking on a Level 90 Overlord, even if he's getting a boost (And if he's getting that boost, then your level 60 characters would die miserably...)?
That would assume Zenon?'s starting level is 90 BEFORE all the plot handicaps. Salome dropped to lv.90 from lv.1400 due to her illness. As for Zenon?, when you finally fought him in the final battle, he wasn't fully recovered from the beating Etna delivered to him, and just got swarmed by a whole bunch other Overlords as well. I would say this is far worse than the handicap that Salome has suffered. (Another similiar example would be Sulfur, who you fight in final battle has only lv.100, but his real level 2000 after he got sent back by Lujie in full strength, he appears as level 100 in final battle because he got handicapped by Sprout)
Actually I'm kind of wondering about that. If levels show so much power plot wise then where the hell are the final bosses in all this. Lamington is only lv 90 for example does this make him some sort of weakling?
For now, I would assume so, Lamington never display the same level of power that's comparable to other high rank overlords.
And by level, I specifically referred to starting levels of the characters. After Phantom Kingdom, there are some clear cut off line.
1500 is the line of top class by average standard. While 2000 is the strongest one can get if you are not Baal.
Also, the difference between 500 and 1500 is much more smaller then the difference between 1500 and 2000. Once you hit 2000, you are basically in a different dimension of power hierarchy (and both Zeta and Rozy demonstrated that VERY well). And the difference between 2000 and 4000 would not need any explanation.
But this is not the only indication of the plot power either. Race matter, as well whether the person holds the position of a Regulator. For example, Valvolga, Alexander, and Pram are Overlords the same time Regulators. This would give them powerful elemental manipulation power that don't universally exists among overlords, and could serve as advantages against enemies that have higher levels then they do. (On even more extreme example, Gajir was be able to enslave beings stronger than him by using his Dominance power as Regulator of World, but he is weak as hell outside that)
Same thing, a level 1500 human might not necessarily capable of defeating a lv.1000 overlord as Overlords universally have cheesy dimensional manipulation power (and by universal I mean even the total failure that is Royal King Dark III posses such power) that can be used for their advantage.
Now, on the topic of lv.1000 ghost vs. Lv.90 Lamington. Who would win, I seriously don't now. What special property a Seraph posses is not well documented. He could have some broken special power like Gajir that allows him to take on creatures who have far more levels than him. On the other hand Ghost is just a Ghost.... and Lv.1000 are item worlds only as well, which basically jumps out of the starting level rules. Baal having a different form in item world shows this very well.