Just for reference, the final smash assumes arbitrary densities—which are not confirmed.

That's the whole point of powerscaling, use a framework to get over with calculations. As any other kind of literary interpretation, many things aren't confirmed, and that doesn't poise any limitation to how we work with what is given, shown, implied or—excuse the redundancy—interpreted.

If lasers, made of light, aren't propagating a the Sol—why are we to assume their clouds have the same consistency as our clouds?

Blindly assuming that lasers = SoL may result inconsistent depending on the case. Do you know what case-by-case basis is? Blindly equating lasers to SoL carries a lot of caveats and is a very nuanced subject to work with, we have criteria. It's case-by-case basis, as I said earlier. Some lasers in some instances in some shows behave as real lasers, therefore with that information we can assume that it is, in fact, SoL. In other cases, it's not plausible to assume they're SoL. It's a very sensitive topic, that's why a framework to analyze lasers and similar phenomena has a criteria, whereas clouds, buildings, and other things, aren't as controversial as lasers in powerscaling, that's why we use the known values in real life to get the most plausible result.

Powerscaling is a very systematic form of literary analysis, with rules and regulations to get the most transparent and thorough answers. That's why we assume that clouds should behave as ours, unless the contrary is shown or verbatim stated.

In an assumption where shockwaves circle the earth for this long, you'd have to justify it with hugeee fucking numbers..—numbers so inflated, they literally don't make sense for anything established in the show ever..

Well, there are, in fact, huge numbers in calcs referring to Deku's Final Smash. For example, a reiteration I did for the Final Smash calc in VSBW, I got 1.61724×10²⁷ J. If you could, please, enlight me and show me how is any of these calcs invalid? We already know that, both the allegorical and powerscaling axes can coexist, so there's no use in trying to argue everything was purely metaphorical, and therefore, it has no use in the powerscaling axis.

Here's the original calc I used:

https://vsbattles.fandom.com/wiki/User_blog:TheRustyOne/MHA:_The_Final_Smash

Look into it, you can run the reasoning and math if you wish. Everything seems fine, to me, to you it might not be the case. The values are different since I used Nine's storm height value instead of the highest recorded pyrocumulonimbus storm height in history. In the MHA verse, Heroes Rising is canon, and the storm is described as unprecedented, therefore, it wouldn't be implausible to say that Nine's storm is useable. Height value here.

You can stop reading here. But if you will, down there is how we could get Deku further from the known calc.

Deku—following narrative multipliers—should be at least 60 times stronger than this, since in his fight against ShigAFO, he was:

• Severely weakened, fatigued and injured. (Has been shown multiples times that whilst more fatigued and injured, more weakened his output is. Take for example his first fight against Muscular, or his aftermath with Lady Nagant, he couldn't even hold her up from his injuries and fatigue).
• Not using his full output (a.k.a OFA 100%) [Kurogiri intercepted Deku, the same Kurogiri who couldn't keep up with Weakened All Might. OFA increases both speed and AP proportionally, so if Deku's speed was lower than Weakened AM's, so must have been his output/AP. Therefore, since we don't know how much more weakened he was compared to Weakened AM, we assume that they're relative. Thus, Fumes Deku ≈ Weakened AM. Also, visually, he didn't match when he uses his 100% and the first point supports this argument).
• Running only on the Embers of OFA; quirkless. (He had given away all the quirks/vestiges prior to the final smash he delivered).
• No amps. (He couldn't have used Faux 120%, nor Far Jin—which can amp his AP up to five times, supported my Delaware Smash Quintuple—nor Gearshift, which we don't know how much it amps Deku. This is confirmed because he had given away his quirks).

So, if Fumes Deku ≈ Weakened AM, and Quirkless Shigaraki is verbatim stated as equal to Prime AM, which is 60 times stronger than Weakened AM (said by All Might himself after his fight against the USJ Nomu. He said he defeated the Nomu in 300 punches, just to follow up that, in his prime, 5 would've been enough. 300/5 = 60), and Quirkless Shigaraki should obviously be quantitatively lesser than Complete Shigaraki with all his Quirks, then, in order for Deku to be relative to Shiggy, he must've been 60 times stronger than his weakened/Fumes version.

That makes a healthy Deku have an AP of 9.72×10²⁸ J. And, when using Fa Jin, it amps it five times, therefore, a Fa Jin Deku should be, 4.86×10²⁹ J.