I don't know how they teach the open G these days (my guitar journey started 30 years ago), but I learned it like you - using fingers 1, 2, and 3. I never really had issues with chord changes. I've seen professionals fret this chord this way also.

What prompted me to learn the fingering with 2, 3, and 4 was a song I had to learn in a church group I played with. In order to play a Gsus4 or Gadd9, you need finger 1 freed up to play the C note on the B string or the A note on the G string.

It felt VERY strange at first since I had been playing 20 years at that point using the 1, 2, 3 fingering. As I recall, it didn't take all that long to get used to. Now I'll use whichever fingering feels comfortable with what I'm playing.

So, I don't think you need to unlearn anything...but learn the alternative fingering because of the flexibility it gives you. Having your index finger freed up with this chord gives you the ability to add some embellishments.