Best way to chart Level correlation to actual metaphysical power output is an inverted bell curve.
Level 0s are unmeasurable or otherwise untestable. Its possible that they have a really rare or exotic power but just plain don't have the metaphysical oomph to make it exist.
Level 1s are invariably extremely weak and limited in power AND function. IF they have a strong function they can barely use it due to drawbacks. Heck, some powers can't be used at all at lower levels.
Levels 2-4 have a lot of room for interpretation, you can be assessed as anywhere within the range, though the closer your power relates to conventional physics, the more likely you are to be ranked correctly.
Anyone remember the girl with the perception invisibility power? Its a pretty complex effect, but super narrow and you could easily justify it as anywhere between 2-4.
Now, remember, most of the people doing the ranking are power development schools and part of the law of the city is that you need to allocate significantly higher funding to higher level students.
Which means if you have someone with a technically potent or exotic power, but don't have the scientists to do anything with it, you really should rank them lower, because you'd otherwise throw money away.
Conversely, if you have someone with a high output power with few research applications, then you might even rank them higher than they really are, because publicity returns funding very efficiently without any infrastructure or staffing demands. Kongou is a good example, her Aero Hand creates an immensely powerful aerokinesis based rocket on contact...and nothing else. No versatility, but in terms of F=MA she can launch stuff which is unrivaled in mass and force below Level 5s. So rank her up.
Level 5 REQUIRES immense computation power and metaphysical power. Theres no doubt about their rank once they use their power for real, because once they start acting they're the most significant person on site.
I personally expect to get into level 2 the next scan after we get rid of the nosebleed, or if they do a scan and confirm that, no, this isn't actually our brain melting down from the load.
For a fun theorycraft, I'd do some projected effects for various ranks and power types.
Teleportation(measurable and easily analyzed):
-Level 0 - Inability to perform either the trajectory computations or the raw lifting power to send anything anywhere on purpose. Small objects may randomly vanish and reappear near you.
-Level 1 - Ability to teleport a small touched object to another location you are physically in contact with.
-Level 2 - Waive one of the limitations on level 1, e.g. teleporting to/from a remote point, or a larger object from one point you are touching to another.
-Level 3 - Waive an additional two limitations from level 2. E.g. Teleport a large object you are touching, or a small object you're not touching. Teleport to a specific reference point(see that guy whose power is to teleport himself directly behind his target)
-Level 4 - Major limitation waiving, so theres a lot of differences. Kuroko for instance doesn't teleport massive objects and she still needs physical contact to teleport anything, but she can sequentially teleport fast enough to 'fly', perform adjustment of orientation(pun not intended), neutralization of exit velocity, and fire her needles as fast as a semiautomatic weapon....by contrast Musujime Awaki puts a lot into teleporting large objects long distances from a distance as a standard action.
-Level 5 - Functionally unlimited teleportation, or at least, the ability to pick which limitations apply rather than being bound to a given set of limitations.
Electron Wave-particle manipulation(Meltdowner's)
-Level 0 - Nothing. Not enough power to be percievable outside of specialized equipment.
-Level 1 - Glow. Nothing more than simulating cherenkov radiation.
-Level 2 - Impossible to measure the difference from level 1 without specialized equipment.
-Level 3 - Generation of intense point heat sources at close range, gets ranked down due to inability to test its extent without slagging herself.
-Level 4 - Ability to direct the point heat sources.
-Level 5 - What we see her do in canon.
The big difference? The sheer magnitude of her ability means that what Meltdowner would need to be measured AS a level 4 pretty much from the start to ever get a fair shake. Without the Parameter List cheating by already knowing what she can do later, Mugino would probably have been stuck as level 1 "make pretty, mildly radioactive lights" without funding.
The power is too hard to control even as a level 5 really.
Its how she lost every single time.
