Hello, my name is Alisha and I have been writing professionally for the past 8 years. I will cut to the chase, following is how I will rewrite the sentence (naturally, this will depend on whether it is a straight-forward rewrite or if there is creative space to elaborate on the topic etc.)
Regardless of who prepares the paperwork, the taxpayer remains responsible for paying his taxes. (this is the one I would use, specifically considering the 'no fluff'.
OR
Even though the taxpayer does not complete his own paperwork, he remains responsible for paying his taxes.
These sentences can be elaborated by incorporating reasons why he does not complete his own paperwork, such as:
The taxpayer is unsure on how to complete his own paperwork and hires an expert to assist him, however he still remain responsible for paying his own taxes.
Should you require any examples of my work, I will gladly send in via the chat interface.
Best regards,
Alisha