You only need arcana for your MC if you encounter it in dialogues, and i dont ever recall any meaningful in any way arcana check i encountered that way. For those 'open world' arcana checks you want a dedicaded wizard which would do them for you, as i said YOU yourself dont get any benefits for having +1 int or any drawbacks of having, say, -7.
I've gotten a couple Arcana and History checks in my most recent playthrough. None of it has been big impact yet but I do still like having it just so my character isn't completely uninformed.
As for open world world checks only needing one Int character? Same could be said for Wisdom and definitely could be said for Charisma. Having more than one character who has a decent Arcana score means you get multiple people rolling dice, which dramatically increases your odds of making the check. Same goes for Perception.
Honestly Charisma is the attribute that you only really need one person with it to get by since no charisma check currently happens outside of one on one dialogue. I'd much rather have three characters with decent INT than three characters with decent CHA.
