You should be using your G Major scale against the G Major backing track. D Major for the D Major backing track, A Major for the A Major backing track etc. You should match your scales against the chord you are playing...
Watch this video series. Around 5 minutes into part 2 Pebber explains why you should play certain scales with certain chords. Once you really saturate the sound of the G Major scale against a G Major backing track you should look to try the scale against different chords/backing tracks. Also take note of how Pebber is singing the notes, playing patterns or picking notes 2-3 times. You want to try different things while playing the scale so you can fully absorb every note of the scale.
On pentatonic scales...they sound good with nearly anything. They have only 5 notes compared to a Major scale with 7. Pentatonic scales essentially get rid of odd or blue notes which might sound strange to the ears of most people like yourself. This is a big reason for its popularity, the scale is the easiest on the ears. But that does not mean you should avoid the Major scale, nor does it mean that you can not play guitar or you 'suck'...your ears are simply not used to the sounds you are hearing.
I strongly suggest you forget about the pentatonic scale for a while and keep focusing on the Major scale. If you have a really good understanding of the major scale then it will make it a lot easier when you begin to look at other scales like minor and pentatonic. It will be also better for your technique, you can get away with using 1-2 fingers on the Pentatonic scale but you will need to use all 4 fingers to play the Major scale well.
Pebber puts up plenty of scale shapes and patterns, these are so you can use as much of your fretboard as possible. But you are right, there is not much point of learning them if they do not sound good. That is why you must persevere with the Major scale and make sure you absorb it completely before playing it against different backing tracks. Your ears will eventually hear things differently, just keep at it.