Based on what they told you,I wouldn't alow either havc tech to work for me. The only problem that oversize duct might cause is uneven cooling in one or more rooms. When that happens,the solution is simple and inexpensive. Uninsulated duct can be expected to sweat. Ducts that are properly insulated do not sweat. The HVAC unit(aka airhandler) is supposed to be properly insulated during manufacturing so I can't imagine why it sweats. The condensation isn't effecting heating or cooling performance. Smells aren't in my wheelhouse.

HVAC duct work should not be wet.

Duct work for a 4 ton unit when having a 3 ton unit would most likely cause performance problems of the system being able to handle the loads of the structure properly. Because the duct system would not be able to pressurize enough to 'throw' the air thru the vents of the structure.

This can also cause longer duct runs to get little to no air.

Duct sizing in and of itself does not cause excessive moisture. Because of where this unit is located leads me to believe that condensate drainage is an after thought for your location.

Usually duct work is undersized, not oversized... because it costs more $$ to over size duct work and most builders skimp.

Some locations require less cooling than heat due to climate. So in fact it could be that the furnace is a 4 ton furnace and the AC is a 3 ton, because for your climate that was all that was needed.

Moisture problems can be complicated, just as much as smell. But your duct work should not be wet. In some instances under high humidity conditions, equipment can sweat. But this should only be temporary condition when dew point temp is occasionally hit causing this condensation to form.... but not to the extent of getting duct work soaked.

Have you measured the humidity level in the crawl space? Most likely it is above 60%. Buy yourself an inexpensive meter or two and take some measurements. You may need to install a dehumidifier. If you can lower the humidity level you should not need to insulate the duct work.

If I were you then I would want a Manual J calculation performed so you can determine the correct sized AC unit that you need for your home. Then I also would see if your ducts were designed using Manual D calculation and sizing. The trick is going to be finding an HVAC contractor that knows how to perform those calculations. Here's a link to Green Building Advisor if you want to read some information on Manual J and Manual D.