What type of ducts are they; what size are they?

It would pay U to buy a low cost anemometer to check airflow from the diffusers. The low cost linked anemometer reads in mph multiply by 88 to get fpm which we use.

If diffusers are 0.187-sf (Ak) * say 550-fpm is 103-CFM. for that diffuser. At that average CFM rate, U would need 14 diffusers. (1400-CFM / 103-CFM= : or 103 * 14= )

A 3.5-ton system should have a total CFM of airflow of at least 1400-CFM.

Here is a link that might be useful: La Crosse anemometer

Yes to all 3 questions but don't change ducts just yet,there are other possibilities that should be investigated as well.
Why isn't the installing contractor making it right? Are you planning to work on this yourself or figure out what's wrong then hire somone to carry out work according to your instructions. If it's the latter,you should find a reliable hvac contractor instead of getting into researching.
If you plan diy,let's get started. Which of these were changed,outdoor condenser,indoor air handler,indoor evaporator coil? Is that unit in picture located in a living area closet or in garage? If in living area,is one or more returns below unit and opening into adjoining rooms? Is any return(s) flex duct? If you simply raise temp setting on t-stat enough to turn indoor fan off,does the outdoor fan stop also? Here's your first assighments. 30 minutes may not be long enough to completly thaw coils,let the fan run 1+ hour then while fan is still running and compressor is off,remove door covering blower motor. Rate difficulty of pulling door open,(A) door falls away after all latches and securing screws are removed (B) door easily pulls away with fingers (C) door pulls away with a little bit of difficulty (D) allmost breaks finger nails or requires screwdriver to break vacum on door.