I hope that's not what he actually said. If he did, find a new teacher :)
..."That is why I'm helping you guys becoming much more fluent than your (or you're?) already are."
No. Horrible in many ways.
..."That is why I'm helping you guys to become much more fluent than you already are."
That will probably make you immediately see your re-cast also cannot have "I'm" or 'becoming' either.
"Become much more fluent than I already am."
Additionally removing 'what' might only be stylistic, but it flows much better without it.
Leaving 'what' in would remind anyone from the UK old enough to remember Morecambe & Wise - Ernie Wise & his intentionally badly worded "Play what I wrote", which was actually turned into a stage play, in tribute.
To re-cast it in much more simple terms, those a native would use without even thinking, I'd also either lose 'already' entirely, or replace it with 'currently'
So, my personal preferred versions, either
"Become much more fluent than I currently am."
"Become much more fluent than I am."
The last is succinct & to the point.
Late thought ...
In the teacher's example - once we've corrected it - leaving the word 'already' in there then becomes encouragement. He believes [& wants you to believe] that you are already fluent & just need guidance to improve still further.
If you refer to yourself in the same way, it could imply boasting.
Using 'currently' or nothing at all leaves out any impression of your own belief in your own skills.