I've heard the rumors are from sources that can't be trusted.
That said, in a hypothetical scenario where it is true, I have two thoughts. The first is I would be glad that at the very least, Lorna isn't stuck around Havok. It's much better for her not to be forced into that position even if it means not being used in the MCU.
But second, it would be extremely telling of the way people think at Marvel. That they decided Havok should show up first even though Lorna was created and got involved with the X-Men before him. And it would demonstrate yet again how Lorna gets exploited and misused to promote Havok but that history never, ever flips around to bring good things for Lorna.
I could also see it happening simply because Marvel's made repeated efforts since 2017 to promote Havok while treating Lorna like she has no worth outside of promoting him and other male characters. Further, it would show just how deep bias runs at Marvel. They like to pretend past comic book fan interest in each character shows their viability for future use in comics. They've used that "logic" to justify why Lorna can't have anything done with her that gives her a spotlight. Yet by that same "logic," they would have to look at and adhere to what Fox did with each character in live action, which shows that there was way more consumer interest in Lorna on Gifted than in Havok on First Class.
To make this clearer: I'm not saying anything against Havok's quality of character for himself or interest he could gain in an ideal scenario. I'm simply laying bare the double standards that would be in play if Marvel decided Havok should get this huge spotlight in the MCU while Lorna gets nothing. If a certain "logic" used to justify screwing Lorna over in comics somehow no longer applies in the MCU, then it's not logic. It's a double standard.
It wasn't proven, it was claimed indirectly by Iceman. That's separate from intent though. I think the intent was "Lorna's now not Magneto's daughter," but I also think the actual original intent of the whole storyline was for Lorna to really be Magneto's daughter.
One thing worth noting in all of this is that Steranko's previously said he worked with Arnold Drake on the story but he felt the collaboration
undercut his creative vision and didn't meet his standards. Steranko has also regularly said the X-Men #50 cover is
one of his top 5 fave covers he did. Notably, Steranko was still on the book for
X-Men #51 but was no longer involved in the X-Men books when
X-Men #52 - which claimed Lorna isn't Magneto's daughter - got published. Meaning that whatever decisions were made behind the scenes whether by Arnold Drake, Marvel editorial, etc, it's highly likely based on Steranko's interest and the timing that Steranko did not agree with the retcon that said Lorna wasn't Magneto's daughter after all.
Given all this, I'd say there's more backing the notion Lorna was always intended to be Magneto's daughter and got retconned out of it than that not being his daughter was the plan all along. Plus, just from a narrative and creative standpoint, it seems very bizarre to spend three issues building up Lorna as this amazing heir of Magneto only to throw in this anticlimactic "lol she's not after all" twist. What point does it serve to put in this work of developing Lorna only to pull "a wizard did it (or in this case, robot)" on her at the last minute.