Scholars and Theologians make this claim because they were imprisoned like Paul was for doing as Paul and to be well known to the Apostle they were traveling because not every Apostle went where Paul did.
But there's other women leaders mentioned in the church.
I commend to you Phebe, our sister, who is a deaconess of the church that is in Cenchr
I'm not sure what you're trying to convey. It's just simply that Junia was well known to the apostles and thought well of (some think Junia can also be a man's name so we're not even sure whether Junia was male or female), but Junia was not an apostle.
I agree with you that Phoebe was a deaconess from Cenchrea (and very helpful to many people). That's what it says in the Bible!