I think both sides make some valid points but I think there's something that everyone seems to have missed and or forgotten. The names can be similar and have a similar process but that doesn't necessarily give them both the exact properties.
Magnetic Confinement Fusion obviously has a lot of science behind it, meaning you should do deeper research into it and see how that compares to Wall's Magic Confinement. Magnetic Confinement Fusion uses Magnetic fields as a big part of its reaction of turning into super hot plasma, which from what I'm aware normal magic is not comparable to forces such as magnetic fields. (Although you could argue that it's just a name and since he's an advanced ass robot he's likely doing the actual thing since we see him making shit like Rail-guns and such. Iirc he also uses Alchemy.) for this part I'd contact
@DontTalkDT since this is his specialty.
Tbh I think the bigger issue is the scaling of it, Wall doesn't use that beam to attack but rather as energy to fuel Etherion and as Pein pointed out, that temperature is very short lived and isn't maintained. Right now Natsu is scaling to that temperature without any actual justifiable reason.
The current reason is pretty ass ngl, Invel's statement doesn't mean that quite literally nobody is capable of melting his ice in his group, especially against attacks that he doesn't even know about. (I.E Wall's Magic Confinement, which he doesn't use as a heat attack but rather as energy to fuel a ******* magic nuke.) but I'm pretty sure Natsu has statements about his heat scaling that you could just use instead since I'm not a big fan of the scaling reason at the moment in time.
So 2 things basically.
1: Talk to DT and see what's valid and what's not valid.
2: Work on that scaling justification. Invel doesn't have knowledge on everything the S12 can do (I also very much doubt his ice wouldn't be melted by August, and Wall doesn't attack people with the 200 million C plasma, he converts it to fuel to power his Etherion.)