New home owner. Let's talk ducting for bathroom fan vent

• 1978 house
• Current vent is about 3" or 4" I believe (didn't measure) and about 25' long
• Vents through the roof
• Replaced bathroom fan with a Broan Invent Series AE80 80CFM with a 4" exit.
• Bathroom fan feels very weak, can't even hold up a piece of toilet paper - lots of moisture in bathroom after a shower.
• Bathroom is about 5' x 13' with 8' ceilings.

piping 1 piping 2 piping 3

I don't really want to replace the vent if I can avoid it. Looks like it could be wrapped in asbestos insulation or something, and the piping diameter looks sufficient enough. Would a higher CFM fan be better? Will the piping strain the motor?

submitted by /u/sct876
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