So I was gonna go on a tirade about how Bowser’s dark power enemies are narratively much stronger than Mario & Luigi’s yet he himself never beats them in both their Toad Town fight and credits fight, which would probably mean that Bowser’s stimulation amps don’t instantly dissipate and last a bit longer. However when collecting the scans needed to show that, I realised I missed a detail that makes the scaling chain a bit more logical.
For the Dark Star fight, it had already absorbed some of Bowser’s genetic code
and grows in size when the battle begins, which may suggest that copying Bowser’s genetic code makes it generally stronger. In the remake
Dark Bowser is only formed after the fight when the Dark Star explodes and begins sucking in more of Bowser’s genetic code, with him also proclaiming he has “not enough [power]”, which basically confirms that the Dark Star was getting stronger from each bit of code absorbed and also seems to retcon Dark Bowser as more of an evolution brought about through enough absorbed code. While none of this is the case in the original game, you can still argue Dark Bowser isn’t a general power boost transformation
as the Dark Star intentionally chooses not to use that form against the Bros. (I’m pretty sure we mainly use the most recent versions of the games anyway so it doesn’t really matter as much what the original says).
Starlow also considers the Dark Star near the beginning of the Airway to be “weak”, only being unapproachable thanks to hax rather than raw power (1:00).
So basically, I think it’s more likely now that the Mario Bros. weren’t actually fighting a half power Dark Star, but instead a half power Dark Star amped by Bowser’s genetic code. The scaling chain is still a bit wonky, but I don’t think the stimulation amp argument is necessary anymore. I think it still means that Bowser is less than 2x stronger than the Bros.
I also wanted to add that after Bowser’s Toad Town fight, he mentions that
he’s still not at his A-game and is still too weak. This was originally supposed to support my new argument, but I’ve completely forgotten how it supports it lol. Still gonna mention it in case it’s important.