Si comparas tus textos antiguos con los de ahora, verás cuánto has mejorado.

In Spanish, real or likely conditions normally use:

si + present indicative + future (or another main verb)

So:

Si comparas..., verás...
= If you compare..., you’ll see...

Spanish does not normally use the future tense after si in this kind of sentence. So si compararás would be wrong here.

Because the sentence is predicting what will happen after the comparison.

• Si comparas... = if you compare...
• verás... = you will see...

It is a straightforward future result: first you compare, then you see the result.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

• comparas = you compare
• verás = you will see
• has mejorado = you have improved

You could say Si tú comparas..., but it is not necessary unless you want emphasis or contrast.