Whether it compresses the insulation or not depends on how much room there is in the bag. With a slim snug cut bag compression of the insulation can be an issue when you put more clothing inside the bag pretty much regardless of the insulation.

Synthetics are a lot better than they used to be, but they are still not as warm for a given weight or volume as compared to down. Also down bags have gotten easier to manage with the advent of DWR fabric and waterproof treated down.

Yes synthetics work better if wet, but I don't find it too much trouble to keep my down bag dry. I think the last time I got a sleeping bag wet enough to be a real problem was around 1980 or so when I was younger and more careless. I have been using a bivy for backpacking and touring in recent years and what little moisture condenses in the bivy collects in three places.

1. A few drops or a tiny puddle collects under the sleeping pad which is inside the bivy. It never touches the sleeping bag is easily shaken out in the morning.
2. A few drops condense inside the bivy on top and is again easily shaken out in the morning.
3. A few drops sometimes are on the outside of the lower half of the sleeping bag shell and are easily brushed or shaken off, especially with a bag with a DWR shell.

If anything I find it easier to deal with moisture when I use a tent.

None of those issues have been enough of an issue to be a worry even on multi month tours or multi week backpacking trips. It is a little extra effort, but honestly I'd treat synthetics the same way any way. Given that I can get by with a bag that packs to the size of a grapefruit and weighs 1 pound 1 ounce. My comparable synthetic bag weighs exactly twice as much and is at least 4 times as much packed volume. They are both useful in a similar range of conditions (I have used both into the teens F when supplemented with some clothing and warm socks)