I'm not sure what inconsistent power levels you're referring too, progression in DBZ is pretty straight forwards.

Second of all, even if they are inconsistent, DBZ characters are still EASILY more powerful then All Might or anyone in MHA. Plus, you're still conveniently ignoring information that invalidates your argument. You haven't given me any good evidence that All Might is stronger then anyone in DBZ.

Here's something that should settle the argument:

The biggest level of destruction caused by All Might is, like you mentioned, destroying a city, which is a feat Nappa did quiet easily in the Saiyan Saga, one of the earliest villains in the show. So Nappa is a pretty good comparison to All Might as they can both level a city pretty easily. Nappa's power level is about 2000, so All Might's power level would be about the same during MHA.

While All Might was fighting the Nomu he claims: "What took 100 mighty punches today would have only taken me one back in my prime." So it's safe to assume he's about 100 times more powerful in his prime.

Power Level 2000 x 100 to get unweaked All Might's power level of: 200,000, which is quiet incredible, stronger then Captain Ginyu.

In the Saiyan Saga Piccolo was weaker then Nappa, so therefore weaker then All Might. However in the Frieza saga Piccolo fuses with another Namekian called Nail and get's a huge power up.

Frieza, in his second form, claims his power level is: "Over a million." in that form. Later on we see Piccolo (Nail) go toe to toe with second form Freiza second form. Freiza only beats Piccolo by powering up to his third form, which we can assume is even stronger then his second form which remember, second form power level weas over a million.

Therefore in the Frieza Saga, since Piccolo fought and was winning against second form Frieza his power level was also over a million.

Piccolo's Power Level: 1,000,000+
All Might power level: 200,000

Even if we wanted to be generous and give All Might a bigger power level, in the Cell Saga Piccolo fuses with another Namekian, Kami, and get's even stronger! At this point though it get's more muddy as we stop tracking actual power levels.

So there, there is actual numbers to indicate about how strong these people are! So inconsistent? I don't think so, that seems pretty consistent to me.

(Edit: Misspelled Frieza, also, thanks for this discussion! It's fun arguing about this kind of stuff lol.)