So are you saying that when Trump said he weighed 215 lbs - he was lying UNDER OATH? Because that's the definition of Perjury...
Because otherwise - it's just like saying that you graduated at the top of your class, with multiple degrees, on a scholarship - while marching with MLK and Mandela in South Africa... Or plagiarizing the speech of some other guy, who was talking about the other guy's wife's family and her history, as if that was your wife's family and her history.
Not that the DoJ would EVER prosecute Joe Biden, for ANYTHING that he totally did - like taking millions in bribes from foreign oligarchs... But, by your standards and definitions, if by some miracle that were to happen, then Joe Biden shouldn't testify, either.
As to the question of testifying in your own defense - aside from the danger of being charged with Perjury - rightly or wrongly - it's pretty rare that a lawyer let's his/her client do that... Because the 5th Amendment prevents your testimony from being compelled - and no matter how innocent you might be, once you've testified, now you can be cross-examined. And that could open up a whole can of worms, no matter what kind of client you're talking about, be they an Angel or a Devil.
So your proposed bet is dumb one, and proves nothing about anything. So, no thanks.