Wet but warm is a typical state when it's 40F-50F, 90% humidity, drizzling all day and tackling 2500 certical feet of switchbacks. Even with the vents open, there is nowhere for the sweat to go.
But you can't count on the warm part. Plainly put, you could die. Bad hiking technique! You need some backup clothing and ways to get warm and dry. If you are going for a run from from home, you can get sloppy with no worries. You might think the same on a day hike and plan on changing back at the car, but if anything goes wrong to delay your return, or you find that you don't tolerate it well, you will find yourself to be a quivering mass of stupid, uncoordinated jello in the middle of nowhere. That's not just unpleasant, it can be life threatening.
So, as policy and practice, you need decent rain gear and a dry layer if you are going to be out all day in cold, wet, high humidity conditions with lots of activity. We would all like to drop the extra weight, but there's no free lunch.
The only effective non-breathable rain gear I know of is a poncho. It's not a bad alternative and gives coverage to the knees and keeps you pack dry too. You get a backup shelter in the bargain.
If you are through hiking or doing a long travel journey, you might need some replacements along the way. Hand laundering can be very effective, although access to a modern dryer may be a problem.