The average defendant in the US is poor or indigent, often lacks much of a formal education, and is usually at the mercy of whatever overworked public defender they were assigned. Go ask any lawyer you know about how much weight their demands carry or how realistic a chance they have of getting evidence that has the patina of scientific certainty thrown out. I bet you discover they have about as much hope of that as a gnat trying to stop a locomotive.
Public defenders are at least politically and professionally incentivized to win cases even if they are not provided the resources to do so. In my county, the appointed defender is private and is paid per case. He is strongly incentivized to take as many cases as possible and spend as little time as possible actually defending people. "Take the plea deal" might be the best advice, but only because the system is rigged against the defendant. You don't have to be poor or indigent, either. The middle class are also in danger and even if they win their case their lives are often ruined and they experience significant financial hardships.
Defendants are weak the state is strong. There is no such thing as a fair trial in this country, holding on to that sort of wishful thinking prevents us from progressing toward anything that approximates fairness.
>Having a public defender represent you when they have hundreds of other cases concurrently is useless.
This could turn into a good thing (for the defendant). Simply argue that the state provided you with incompetent representation and therefore any continued proceedings by the court are unconstitutional.
Or, at least getting every piece of "non-science" evidence thrown out?