No it isn't. If anything it shows that he didn't want to endure his potential punishment. If he didn't understand the potential punishment there would be no need to commit suicide.
Your statement could be misinterpreted to mean that any rational competent defendant would consider the potential punishment worse than death.
I'm positive that you meant that he understood what 35 years in jail and a felony charge meant and was thus not unfit to stand trial under an insanity claim. That's fair.