You need skin excision. I would not tighten the diastasis recti. The skin excision will get rid of the flaccid skin and the scar will be hidden by underwear. The umbilicus stays the same location, the skin above it rotates downward.
How does your breasts look when you raise your arms above your head. The muscle may simply be in spasm, or they are being pushed up because the pocket needs to be expanded for the lower pole.
Two questions: did you have a normal pre-op mammogram? Did you have a hematoma (alot of bruising on that side). This may be just a local problem, of old blood oozing out of a small area. Take a photo and resubmit your question
The implants are perfectly aligned behind the nipples. Great job. When they were first put in, the implants ride high because the implants behind the muscle can only push the implant up, and as the muscle relaxes, it jobs, but they are perfectly aligned.
Breasts are not bottoming out. Doing a mastopexy (lift) and breast augmentation is one of the hardest procedures we do. Because you are adjusting three parameters at the same time. The body always relaxes a little so the upper pole fullness which patients loves relaxes. Your scars are excellent and the size is also very good. As I tell my patients, what goes up comes down, so with time, you can always retighten the incisions. Enjoy your breasts.