Only formal mathematics exists. Informal mathematics is just wrong and useless.
Is informalized mathematics wrong and useless, as it is informal and has not been formalized? If you assert so, then mathematics as a field of thought must be static: this means its development always follows a rigid and eternally consistent process, yet this process itself is unchangeable and inherent to the meaning of "mathematics." In that case, you can not let yourself to believe its incompleteness promises to consistently develop all possible solutions when targeted for practice by an interpretation. Continue by reading: https://en.wikipedia.org/wiki/Completeness#Logical_completeness
Please consider studying Lee Smolin's view on mathematics. He explains a philosophy which is very much concurrent to mine. Of course, I do have my own fanatical quirks appart from him.
It looks like you have read too many philosophical books, but you have no knowledge of mathematics. Without a formal proof, any conjecture is useless and meaningless. But having constraints does not necessarily make something static. Think about music or sculpture or other form of arts. They have a lot of physical constraints and rules, are they static fields? Think about literature, you have to write in a grammatically and syntactically correct way. Is literature static? Mathematics is a very creative and vast field. There is really no rigid and eternally consistent process.
The funny thing of your statement is that most mathematicians do not care at all about logic or set theoretic problems. Those fields are not so important and logical completeness has no effect on the daily work of a mathematician. I have seen more computer scientists work on such problems than mathematicians. But really, is there any reason to separate those category so strictly?
On the other hand, there seems to be no sensible reason not to use mathematics. Or can you name even a single one to back up your statement?
The burden is on you. You even have a contender.
If do not have any reason to back up your statement, then it is false. No one here think it is true and we have already given some arguments supporting our thesis.