You are missing the point, the old method to downgrade to 4.5 results in 4.5 system. This method only downgrade system settings. They aren't in any way the same.
Also, I don't think they would need to port the cubic ninja or Zelda support for old 3ds for this. It is is only used as an entry point the first time to install the CIA. But we can always use the online method instead as an entry point and install the CIA.
Again, that's how I understand it, unless I am missing something
No, because those 3DS that can't use gateway is because they don't have a working browser (never got updated through internet) so their only way to run gateway would be to see the Cubic Ninja/Ocarina of Time exploit ported on them. If they had a working browser, they could use the online exploit then downgrade if they want the DS profile exploit.
So without a working exploit, they wouldn't be able to use this mset thing. Like on N3DS, if you don't have Cubic Ninja/Ocarina of Time, it won't work because you don't have a working exploit to install it.
But if they port the Cubic Ninja/Ocarina of Time on the O3DS, you won't need this mset thing as you would then be able to either use the Cubic Ninja/Ocarina of Time exploit, or downgrade directly to 4.5 if you want the DS profile exploit.
I know this methos only change the system settings and it's because a N3DS can't be downgraded. But on an O3DS, there is not point in using such a thing when you can directly downgrade to get the "true" ds profile exploit.