System Replacement Suggestions for SoCal dual vs single stage

We currently have a weird setup that is uncomfortable and expensive to run. House us 1950 sq ft. The system is way to oversized and it is 5 ton. It is in the garage and the majn trunk goes uo into the attic. The two closets, largest and shortest routes are on the 1st floor. When it calls for heat or cold, it is like a jet engine and majority of air pushed into the 1st floor. One area is 25x18 and has vaulted ceiling so it is not as bad. Other room is 15x18 and that gets either super cold or hot. Due to this, less air goes upstairs and the ducting for that is not great since most air us pushed into the 2 bathrooms and not the 4 bedrooms. I havw few guys come out to give estimates and so far have two estimates. Both basically suggested the same thing. Lower the size of the units, add permanent dampers on 1st floor to push less air into the 1st floor, andd adjustable dampers to the 2nd floor bathroom ducts to push more air into the rooms. One estimate is a for a 3.5 ton AC, 4 ton furnace single stage for 15k, all Carrier (if i decline permits it is 1k discount) Second one is for 15600 for single stage 3 ton for both, 16700 for dual stage 3 ton or 71400 for 4 ton dual stage. First company thinks dual stage is not needed. 2nd one thinks 3 is enough but if we go to 4, dual stage would be better. I doubt any actual j load was done. Just rough size estimate with updated insulation and windows for houses built in the same age as mine. No real room by room measurement. I am in SoCal so winters are very mild but summers can be hot but not super humid. It us more humid when it is cooler Any suggestions?