It's all about sound.
A-dorian got the same notes as G-major so when you just look at note names
in the two scales, it's just the same.
But when you use your ears, A-dorian is someting very different from G-major.
If A-dorian is played against a A root and G-major is played against a G root.
I would say it is very wrong to think of playing in A-dorian when you are
playing G-major. But if that works for you, just go that way.
My advice, record a G drone note that last e.g 3 minutes.
And try to play some G-major scale stuff over that.
You should hear the "major sound".
Then play some G-dorian scale stuff and you should hear the "dorian sound". A new world.
Then play G-mixolydian, a new sound/world again.
And so keep going with all kind of scales, they are all from different worlds.
I know many people like to think of major whatever mode they are really playing.
Because they know how to play in the "major box".
But when you one day later are gone play a G#-Egyptian/Indian/or whatever not church mode scale
what major scale box are you then gone use? There are no one to use because you are not
playing any church modes. So the only way to go is to learn the scale, the structure, the intervals and
the sound. Trust your ears. Practice practice practice, no simple easy way.
Well you could maybe sell your soul to the devil, but I would prefer hard work