"I think those claims are unsubstantiated due to lack of sufficient evidence" or even "I think those claims are unsubstantiated" alone comes across better than "pretty sure you're making that up".
Best not to be 'pretty sure' with accusations, even mild ones, especially when you're apparently wrong. And why are you pretty sure? Seems like you have some reasoning, mention why with your accusation or your viewpoint will be 0 on the contribution scale. It comes across like a child discussing whether or not he thinks Santa is real "Yea I'm pretty sure he exists and you're making it up"
Best not to be 'pretty sure' with accusations, even mild ones, especially when you're apparently wrong. And why are you pretty sure? Seems like you have some reasoning, mention why with your accusation or your viewpoint will be 0 on the contribution scale. It comes across like a child discussing whether or not he thinks Santa is real "Yea I'm pretty sure he exists and you're making it up"