Right now, your code is meta (most efficient tactic available with only GDScript). The problem is with GDScript you can't use an override, you are indeed right. However, as the Document says (if you actually read them) C# is 3x faster than GDScript.
GDScript (Release) 13820
C#/Mono 48680
GDNative (Nim) 52780
GDNative (D) 57360
GDNative (C++) 58120
The above is a benchmark on the amount of Sprites loaded and called using a function by spawning in objects and setting their texture to the files recursively. C# is 2nd to best, While GDScript is insufficient. Please be aware than using both Languages (as many professional programmers use more than 1) is not a downside. In a Computer Science class it fails the basic algorithm design in the designing process because we're striving to have most efficient and quickest algorithm available. So take the time to learn both of these languages it will be beneficial in the future!
Don't be a one-trick.