No. That's still just backscaling, and doesn't work.
If you establish that he scales above these characters' combined attack, you can't then scale them to someone that scales to these characters.
Plus, it doesn't even matter how good the vessel was.
BDK had the life in Britannia, which is stated to have a lot of magic power.
All it did was explode. Nothing suggests he even somewhat matched it. Also, he already scales above someone just 2x weaker than this, so it already makes enough sense in the scaling.
Sure, but that would just downgrade Gloxnina 2 to 3 fold from Demon Meliodas.