I would hope you see the problem with your assertion.
There is no way I can KNOW you exist and are making the assertion. There is no way anyone other than you can KNOW you exist and are making the assertion. All we can do is guess.
And for you to suppose you can KNOW that in order for me to make an assertion...I must exist...is also a guess (not a good one at that). I may simply be part of the illusion in which you are "existing"...and any assertions I supposedly make may be nothing more than extensions of that illusion.
You are attempting to apply to me (and to the others out here) what (supposedly) applies to you. But there is no logic in doing that.
I can "make" any assertions I want...and you have no way to verify that I exist. I may be "making those assertions" without existing...being merely an extension of an illusion of which you are part. YOU may be making the assertion supposedly I am making.
So while your "assertion" that you must exist to make an assertion has applicability for you...your application of it to others does not.