As a certified licensed home inspector it is not correct to say too much ventilation is bad for an attic unless rain moisture is.
Attic too hot for ac.
Furnace coil and ducts are in the attic in a very hot environment apparently somewhere in the furnace the air gains 4 to 5 degrees and maybe 1 or 2 degrees more in the ductwork.
And it can cause your air conditioner to work harder than it needs to and send your energy bills soaring with the temperature.
Low cfm similar to a bathroom vent 300cfm and only in the hot spots basically by adding an inline ducting fan to the return ducts for the hotspot rooms.
Having a properly vented attic is the best way to keep attic cool because it allows the hot air to escape during the summer.
An overheated attic can bake asphalt shingles on the roof and cause them to deteriorate.
Hang pencil and paper next to the thermometer and record the outdoor and attic temperatures.
My idea is to vent the build up of hot air that has risen to the ceiling in the hotspot rooms into the attic so that air from cooler parts of the house can move in.
In addition hot air in your attic could increase moisture levels which could result in wood rot and mold growth.
An unventilated attic can reach 150 degrees in the heat of summer 50 degrees higher than it should be.
Hang an outdoor thermometer in your attic making sure its range reaches at least 130 degrees fahrenheit.