That or FGO's system is wholly different than the other Grail Systems?(Something that has been true since any Grail System outside of Fuyuki's?) Or the fact that it's gameplay and outside of referencing it a few times in the past, it doesn't really matter in canon? I know it depends on the person but it's ultimately a worthless affair that doesn't defeat the point of what happened to U-Olga Marie.
That's only in the most base of terms that Artoria isn't Saber or Cu isn't Lancer, they are Heroic Spirits put in limited Classes that does not reflect their entire legend or even their person at large. Lancer Artoria isn't the same as Saber Artoria and Cu isn't the same as his Caster Counterpart, Setanta or his Altered Berserker self.
That does not or will not matter in comparison to the situation with U-Olga.
Because that's the point of a mystery, my dudes... we know that U-Olga has a Noble Phantasm but it's liked in a way that you can never see it even with hacks. All we know is that she has a "Rainbow" Classification once she gets amnesia, she's Beast VII in Olympus but curiously, she isn't Beast VII in LB7 even before she lost consciousness:
U-Olga Marie (U-オルガマリー??), also known as the Alien God (異星の神, Isei no Kami??), is the main antagonist of Cosmos in the Lostbelt. It is the unknown entity who resurrected Crypters, bleached the world and set up the competition between Lostbelts, with the winner supposedly inheriting Human Order...
fategrandorder.fandom.com
She doesn't even have a Nega-Skill or Authority of The Beast which are MUSTS for any Beast but she has
Defender of Humanity... and again, this is when you fight her in LB7.
So yeah, this is really a pointless thing Lucain is being in but SB boys never know when to quit when obvious information comes in and debunks their point.