You would be correct if that is all the prosecution has.
However they also have, according to the court documents, the testimony of David Pecker (AMI Media), the testimony of Allen Weisseilberg (Trump Organization Chief Financial Officer), other testimony, texts, emails, contemporaneous notes, invoices, business ledgers, checks, etc.
Then of course we know that Cohen was known to make audio records of phone calls. One of which concerning Karen McDougal is already in the public sphere. Are the others? Considering Cohen was Trump’s fixer and Cohen probably recognized the need for CYA regarding Trump, probably better than 50/50 there are more tapes.
So one would think that a DA charging an ex-President would have much more that the word of one man.
Time will tell if the DA has his ducks in a row.
WW