We have both down synthetic bags, and each has their place and season.
I do love the weight and compressibility of down, but will offer a peculiar take on down vs synthetic. I am a warm sleeper, and early to bed (and read) when solo. The temperature at dark is often 20 – 30 degrees warmer than it will be at dawn. Your location mileage may vary.
If I have been bustling around, last check securing camp before bed, I am as warmed up when I climb into the tent as I’ll be all night.
Add to that I am a side sleeper, turning to change sides and that becomes a helix twisted mess when zipped up, especially in a mummy bag. I bring a bag one season warmer than anticipated conditions, simply draping over me a quilt. If it gets unexpectedly cold I’ll give in and zip it up, or at least partially zip it up for a foot/leg box.
With the ability to regulate my warmth by sticking out feet or legs, or even just torso barely covered by the bag, I gradually cocoon as I cool down and the night gets colder. Probably helps to reduce overheated moisture in the bag.
For tucked in around the contours of my body in chill of night a synthetic bag works much better than a more weightless down bag. The heavier synthetic material drapes more closely around by body, without lofting chilly side channels /0\ near the pad.