To cheat, the party hosting it would probably have to forge signatures for everyone after the disputed signature.
The fundamental challenge here is that there's no way to tell, based on a the signature alone, which signatures are "valid" and which are "forged"; they're not cryptographic signatures. And getting cryptographic signatures for lay people is apparently too hard to do, outside of Estonia's digital citizenship initiatives.
It might be neat if the big guys agreed on an OIDC extension that let you piggyback text to be affirmed by the user. Cryptographic proof that [email protected] saw text with hash H at time T and chose "Accept".
This seems like the claim that the USG will be unlikely to put it's Military on the line so they won't leak any tank designs on discord.
Happy to concede that the CEO of DocuSign wouldn't do this but surely some 15$/h employee doesn't have that same opinion.
The non-custodial party can claim they never signed, and when the custodial party produces evidence of IP address and timestamp, the non-custodial party may have a credible argument that they are faked and the person asserting those authenticated details has the motive and means to fake them.
That argument is much harder to assert with something like DocuSign because it is unlikely DocuSign would put their business on the line to fake someone's signature.
I'm not saying repudiation based on custody of the e-signature platform is a winning argument, but it's something to consider before self-hosting if you are going to use the platform to sign your own contracts.