Concerns after Reverse Total Shoulder Replacement

Hello, I'm new to this forum.

I'm 55 yo, and I'm just over 6 weeks post Reverse total shoulder replacement. I am concerned. I have not contacted my surgeons office yet because I don't want to complain without more facts.

My rotator cuff and all associated movement/external rotation etc was perfect before the surgery, and now it seems it's destroyed. (please read on).

I've been dealing with bone on bone shoulder arthritis for years, (heavy weight lifter off/on over the years) and finally decided to get it done and over with ( also, now is a good time because of other life situations).

Every assessment of my rotator cuff per-surgery was that it was good. I've never had any issues with rotator cuff, very strong. So I went into the surgery, and was literally in pre-op with the understanding I was going to have a standard anatomic total shoulder replacement, with a possible need for a custom made augmented socket insert (to compensate for some socket wear). I never had an MRI pre surgery, because the surgeon said once he's in the shoulder during surgery, he'll be able to much better assess the condition of my rotator cuff.
In the recovery room after surgery, is when I hear they had to do a reverse total shoulder, because apparently my socket was so worn down . That upsets me, because why didn't the CT scan show them before the surgery that the socket was so worn? And that I was expected to have a Reverse Total Shoulder Replacement? And then, what the ramifications of that will be e.g., big loss of use of dominate arm. The facility touts they use "Blueprint 3d Planning + PSI" that "creates an anatomic 3D model of your shoulder and virtually perform your shoulder replacement surgery"

If that's the case, why didn't they know ahead of time that I needed a Reverse Total Shoulder.

The point is, my rotator cuff and all associated movement/external rotation etc was perfect before the surgery, and now it seems it's destroyed. Even though I'm only barely over six weeks post op, I have no external rotation with "positive elbow flexion". In other words, I can't hold my elbow straight out in from of me, with arm bent at 90 degrees. Elbow will push outward, I can't keep in near my body.(SEE PICTURE BELOW).
Even sitting straight upright, at a table, with elbows very slightly in front of me (like now at a keyboard), I have to external rotation. The surgery was performed on my left shoulder and I'm left-handed. I have to hold my dominant arm so that I can brush my teeth, shave, even eat. If that doesn't get any better, it'll be a disaster. I'm already wishing I had my arthritis back. 🙁

I will be angry if they knew ahead of surgery that I needed a Reverse total shoulder replacement, while also having a perfectly good rotator cuff, and didn't tell me that I will lose a lot of use of my dominate arm.

Again, I'm sure people will read this and say ....."hey you're not even two months post surgery, give it time to heal", ......but other aspects of my recovery (Active range of motion) are going very well and this external rotation thing is not at all. If it was going to improve, I would think it would have started improving by now.

I'm hoping that somebody here who has had a reverse shoulder replacement can address external rotation ability. Again from my perspective, my rotator cuff was perfect. I had no limitations whatsoever, and now I'm afraid the use of my dominant arm will be much worse than before the surgery. I am making very quick recovery in all other aspects.

attached is picture of left arm. Can't move it outward. It's not because it's sore, it's just there is nothing there to move the arm.
Seems doubtful it will improve but looking for feedback.

Thanks all