I kinda see the diff naming as more of Guest difficulty here. But as a group instead of individual. GD also need the player to search who's the guest mapper if they want to know. In a sense, a group is also the same.
In monstrata's case, he was using someone's name that never map the diff in the first place as GD, but this map actually using group that all the member has contributed to the map in some extent, both are different.
For me I 'd love having the current diff naming, It kinda emphasize more on the map that just won contest that's been acknowledged from the osu staff (since the title given only can exist if the contest got approved).
Also not everyone can win anyway, I' would prefer winning map that other player will at least be remembered more and special on its way for winning instead of using plain collab / normal - extra all over again and blend with other rank map in general.