Samsung camera was vastly improved with updates really. What version of gcam and what settings config are you using?
My Scam gallery of late:
https://imgur.com/gallery/2SYhNxV
Those are some nice pics but I have the latest OS and app updates, and no matter what settings I play with in the app, there's details always turn out as a muddy blur with oversharpening. Here's a good example comparison:
Samsung Camera (Bixby Scene Optimiser on)
GCam 7.3.018 Urnyx05 v2.1 with "s10-config-v2"
The images are cropped from the originals but you don't have to even zoom to see the huge difference. The leaves and bark are just a blurry mess with Samsung Camera, and you can see sharpening artefacts around the bin.
Maybe with good light Samsung Camera is much better?
Btw no OEM phone allows you to remap the double tap power button to launch an alternative camera app so not a niggle specific to Samsung.
I think the double tap setting is only in the Samsung Camera app, it's not actually a system-wide setting. If it was, maybe it could be changed.
Totes jelly of you Snapdragon users having the option of GCAM.
Also is it not just possible to map the Bixby button to launch it?
I am able to do this on my OP8 Pro with gcam installed. I double press power and get list of apps to open camera on. I'll the just tap once and open camera app.
Bixby remapping works but basically Samsung has locked down what can and cannot be done from the lock screen. The default camera app also cannot be changed as far as I know...these two restrictions are probably one and the same, i.e. only the default camera app can be launched while the screen is locked, and they don't let you change that app. With LineageOS I was able to use any camera app. It's a crappy Samsung restriction, just like not being able to change what gallery app is launched from their camera app.
I currently have Bixby set to launch Samsung Camera from lock screen and GCam when unlocked (plus long press for torch and double tap for night mode). Even that isn't perfect though because right now I prefer to take videos with Samsung Camera and photos with GCam. >_>