It would be VERY helpful and a huge time saver if we could assign groups to members from the members profile. Going into every group and adding members takes to long.
I might be misunderstanding your idea, but you can manage group membership from the "Organization > Members" section in AGOL. You just select the members you want to manage group membership for. Then, with those users selected, click "Manage Group Membership" (it might be hidden and you'll need to click "More > Manage Group Membership.")
Then, you can select all the groups you want to add the user to all at once instead of going to each individual group and adding them that way.