The attacks aren't aimed at the criticism of Biden. They're aimed at the result of that criticism. People want everyone who reads that criticism to understand that, obviously, Trump is worse in many, many ways, even if he were the same as Biden on Palestine.
He isn't the same. He's worse and has said as much. Leading politicians in his party have suggested using nukes on Palestine, etc. etc. But even being equal on this one point, he'd still be so much worse overall for everyone. So people want to stop those potential outcomes of criticism, not the criticism.