Underperforming Fujitsu mini-split repair/improvements

Hi - looking to make some improvements to an existing Fujitsu mini-split system in Brooklyn, NY

Current setup - we have 3x AOU24RLXFZ units outside, each servicing one floor of a 3-floor row house (about 700 sqft per floor). Inside we have 2x ARU12RLF in a finished basement, 2x ARU9RLF on the middle floor, and 3 x ARU9RLF on the top floor.

One of the AOU24RLXFZ units needs replacement (out of warranty), so that is the motivation for improvements but we always struggle to cool the top floor effectively in summer, even running 24/7 at coolest settings. One contractor we spoke to last year suggested the top floor system was under-powered considering the room sizes/ceiling heights/skylights, because it’s the top floor, and because the AOU24RLXFZ capacity was being stretched with 3x ARU9RLF.

Does this seem feasible? If so, what would be the best approach to improve things on the top floor?

1. Replace the AOU24RLXFZ with an AOU36RLXFZ1? Would the 3x ARU9RLF still struggle with the space? Perhaps a good first step as no interior work would be required.
2. Replace the 3x ARU9RLF with 3x ARU12RLF? Assume this means the AOU24RLXFZ would also need to be replaced with an AOU36RLXFZ1 anyway.
3. Any other suggestions greatly appreciated!

source https://hvac-talk.com/vbb/threads/2227076-Underperforming-Fujitsu-mini-split-repair-improvements?goto=newpost