There should be nothing touching the vent pipe other than non combustable materials such as metal or ductboard.Must have 1" clearance from all wood so plastic aint gonna cut it.

The only way to know is to test the CFM with a meter. You should get the near rated CFM for a straight horizontal run of duct. I have a 115 CFM Panasonic fan in my bathroom that, like you, is a straight horizontal run out to the wall, about 4 feet, through 4" rigid duct. I installed it myself and put a louvered vent cover on the outside wall. I thought it was working well until I brought an energy audit guy in and he only measured 60 CFM. The fan seemed to be working fine so I went outside and took off the vent cover. The CFM jumped to 112. Regardless of your ducting, make sure your vent cover outside is not hindering the air flow. My old vent cover was fine mesh with louvered metal slots. I replaced it with 1/4" mesh wire and nothing else. I have yet to find a permanent cover, but the fan now works really well and is even more quiet.

Properly installed ducts will not sweat regardless of how humid surrounding air is. One red flag in your discription is "cheap tape was used". Flex duct is best secured with Zip-ties. The linner is normally taped to boot then insulation and outside cover pulled over linner and secured with Zip-tie. If you reconnect ducts to boots,buy the special tensioning tool to pull Zip-ties tight. It sounds like conditioned air is finding it's way out of the spirial wire linner then flowing against outside cover. There might be holes in linner or linner might be disconnected from boots. Another possibility is that duct is simply not well enough insulated.

I wasn't being sarcastic. That hole looks way too small for a squirrel or rat. But I was thinking energy only. A cat can get through an opening just 3 inches wide. A squirrel needs only 1½ inches. A raccoon can get through a space 4 inches wide. The reason this seems so improbable is that their bodies just look too darn big to fit. But that’s all show — a lot of hair or fur covering a very scrawny little body. Now here comes the part that could give some people nightmares. Mice need a hole only about a quarter-inch wide and young, slender rats can zip through a space as small as a half inch. We’re talking the size of a dime for mice and a quarter for rats. Not all rats can fit through a space that small. Older, plumper rats need a about an inch. Some people say rats and mice are so good at this because they can collapse their rib cages, but that’s a myth. These animals simply are sleek, cylindrical creatures accustomed to navigating narrow spaces. And as with other animals, if their heads fit, their bodies will follow. (reference: https://www.mercurynews.com/2013/11/27/morris-big-creatures-fit-through-tiny-openings/ ) A vented attic has daylight all over. True. However, these openings are covered with vent screens... if not you're asking for trouble.