I only got to watch Princess Promenade with my sister in a roadtrip when I was 11, and I remember thinking it Wysteria and all the cast was super cute
I haven't watched anything other than G4, but I think the best way I can describe G3 is "they all are extremely huggable". They all are adorable, and what I've seen from videos like that compilation of Minty being autistic they make me feel a weird comfort and cuteness G4 really never made me feel.
I kinda understand now why most of the girls at my school and my sister were so attached to the G3 ponies; the ponies and the specials are very comforting and pacifying, and any little girl would want them as their friends.