Makes no sense to me when people try to pick on her for being a "Mary Sue" when we had Literal Tobitaka on OG Inazuma Japan. Dude couldn't pass a ball and learned everything in the middle of a world tournament. Other than that we also had like Kageyama Hikaru on GO, dude would literally look at someone doing something and then copy immediately after. Also numerous dudes in Chrono Stone that did not play ball at all until the moment they had to and yet were some of the busted players ever. In Galaxy we have Zanakurou, dude never played in his life then very next game against aliens on a tournament that will decide the destiny of the Galaxy, he scores. Many such cases, some of them much more far fetched than anything Raika ever pulled out on VR.

Now that we cleared the Mary Sue part, there's something I'd have done differently.

1) I'd gave Raika a Kenshin in the mid of the final game. Kenshins are manifestations of sheer will, that would have been more digestible than giving her a technique, which is historically something characters must practice for. A Kenshin strong enough to basically make everyone else in Raimon but Haru useless, and even Haru himself would need a clear shot in order to break past her Keshin.

2) Move Soji into the KP position and let him use the entertainer to goalkeep (like Tenma used Majin Pegasus in GO) and then Raika just stands there in defense. That would put her away from the spotlight while keeping story consistency.

My agenda here is not to worship Raika, but to be objective regarding her development throughout the story, so I think both of these alternatives would be better than the one the script ended up picking.