My left palm slightly supports my neck to counter neck dive and also because it feels right. When I play an open G string though I have to open my left hand to avoid muting the string, and my neck moves forward, no pressure on the front of the neck to counter the slight thumb pressure on the back. It feels very artificial and impractical to press a finger onto a lower (visually higher) string, and so I end up with the neck going forward and getting pulled back when I use the open G string. Should I just get used to it?
You shouldn’t need to apply much if any thumb pressure on the back of the neck. It should rest very lightly.
If the bass is properly set up, you should be able to cleanly fret notes without having your thumb touch the back of the neck at all, with maybe slight counterpressure from your right forearm on the body of the bass if needed.
In fact this is a useful fretting exercise at the start of a practice session; slowly play a few scales without touching the back of the neck. It will be difficult at first but it is nice for seeing just how lightly you need to push to fret notes.
A light touch is the key to playing smoothly and faster.
Also, you shouldn’t have to use your fretting hand to prevent the neck from dropping. Some basses just have neck dive, but this can usually be countered by using a wider strap, and/or one that’s made of a material that provides more friction against your body. Ideally, the bass should stay in place without having to touch it with your hands at all.
Along with a good wide strap, you can position your plucking arm to rest on the lower bout of the body to counter-balance neck dive.
If both a strap and your arm are not enough to do this, you have a severe case of neck dive.
Installing lighter tuners will help a lot. But if it doesn’t fix things, you will likely need to reposition the lower strap button so your bass hangs at a higher natural angle.
This usually completely solves the problem, maybe with the addition of a high-mass bridge too. If the neck dive is bad to the point that these won’t fix it, there’s a serious issue with the balance of that instrument.