I don't know. Both of the characters have varying powersets which overlap Carol's. Jessica has the superhuman strength and energy projection. Monica doesn't really have superhuman strength, but has energy projection. Monica's ability to fly at the speed of light and access various energies across the EM spectrum are more in line with Carol's binary powers.
Powers aside, Jessica Drew worked with SWORD(The space version of shield). With that background, I could clearly see Jessica crossing paths with Carol. After Earth is warned about Thanos, something like SWORD is established to defend against extraterrestrial threats. Carol and Jessica are some of the first recruits.
I really don't see the problem with the differing power levels between Carol and Jessica. Keep in mind that the Avengers have mere mortals like Black Widow and Hawekeye fighting alongside giants like Thor and Hulk. So far, Marvel has done a great job of keeping with established comic book friendships. I just don't want to see them deviate from that.
Marvel is even willing to change things up to make the established friendships seem more fluid and organic. Take Falcon, for example. They changed up his origin to make him a military guy. That works perfectly for his relationship with Cap as a fellow war buddy. They hit it off right away, because they understand each other so well. They can talk about those things that nobody else could possibly understand.
I have no problem with Monica and I wouldn't mind seeing her in the Captain Marvel movie. She just doesn't have the established Captain Marvel had with Spider- Woman.
I think you misunderstood the initial points. Nobody is saying Spider-Woman is unlikely to appear because she's weaker than Carol. We're saying she's unlikely to appear because she is a completely separate character from a separate franchise with origin story that needs to be explained, which they're not going to do in Carol's first solo outing.
If you've noticed, there's a distinct trend with these films. They introduce the lead hero and focus on him or her, and then the sidekick or additional heroes in the sequel. Iron Man 1 was about Tony and Rhodey just appeared as his best friend. In the sequel, he gets his own suit and becomes a superhero in his own right.
The first Captain America was about Steve, then in the sequel we meet Falcon and Agent 13 and have Black Widow join the cast.
In Ant-Man, the movie is about Scott Lang, and Hope only appears as a civilian member of his heist crew who trains him. Now they've set it up so that in the sequel, she gets her own powers and becomes the Wasp.
Marvel likes to keep things relatively streamlined and simple in the first flick, which is why we're saying it's unlikely Spider-Woman will be showing up and why it's more likely that if they want to give Carol a friend, it'll be someone easier to work into the premise like a not-yet-powered Monica or even just someone from Carol's supporting cast.
While you are correct in saying she could appear as a member of S.W.O.R.D., there's no guarantee S.W.O.R.D. will be in the movie or play a significant role. Remember, it was said not too long ago that Marvel doesn't even have the film rights to the S.W.O.R.D. organization.
