Your example:
The more the sincere one's effort is, the faster their growth is.
is very close. There are two fixes you need:
you have an extra "the" in the first one. I'll show some examples below.
the subject changes from "one" to "their". This is a violation of parallelism. Parallelism just means that between parts (1) and (2), when things are the same, their parts of speech, verbs, singular and plural, tenses, etc. should be the same.
The more, the more
Here's a simple example of "the more..the more". It is common to use the word "more" twice.
- ✔️ Yes: The
more
you do, the more
you get.
- ✔️ Yes: The
more
I work, the more
I earn.
- ✔️ Yes: The
more
I work, the more
that I earn.
- ✔️ Yes: The
more
I work, the more
money I make.
These are a little awkward:
- 😐 OK: The
more
I work, the more
money that I make.
- 🙁 Not good: The
more
I work, the more
that I make money.
You can even use "more" and "less".
- Yes: The
more
I learn, the less
I know.
In each example, notice how the subject doesn't change its form (you...you)
, (I..I)
. The tense does not change, either.
Comparisons without more
You can do the comparison without the more:
- Yes:
The slower
I work, the poorer
I get.
- Yes:
The faster
I work, the richer
I get.
You can do the comparison with just one "more", but it is not usual, and does not sound quite as good:
Maybe: The faster
I work, the more money I make.
Maybe: The more money I want, the harder
I look for work.
Parallelism is your friend
See if you can tell which ones sound best:
- (A) The more you work, the more you earn.
- (B) The more you work, the more money you will earn.
- (C) The more hours you work, the more money you earn.
To the native ear, (A) and (C) sound the best because their parallelism is better. (B) is not necessarily wrong, but it sounds weird.
The more, the more
You can see all of this in a dictionary example:
the more (one thing happens), the more (another thing happens)
An increase in one thing (an action, occurrence, etc.) causes or correlates to an increase in another thing.
[1] The more work you do now
, the more free time you'll [you will] have this weekend
.
[2] The more money we make
, the more responsibilities we get
.
-- Farlex, The Free Dictionary (emphasis added)
In sentence [2], notice how both parts have "we" as their subject, and they both use the same structure -- "we + verb". The verb is present tense in both cases.
Tense changes
In sentence [1], the construction is more tricky, but it is valid.
- The tense changes from something happening now (present tense) to the future (future tense).
This is fine, but there needs to be a reason:
- Yes: The more I run today, the better I will feel tomorrow.
It's clear that a present action has a future result.
- No: The more you work, the more you will earn.
Why the tense shift? It's not clear why the second part became the future. Stick to the same tense, usually.