How many botched prosecutions are there? Most have a 90%+ conviction rate because normal people can't stand up to professional interrogation. Even innocent people can incriminate themselves to the point where it isn't worth the risk of trial, so they plead to a lesser offense.
Spend thousands going to court and possible spending 5 years in jail vs. plead out for probation. The fact that going to court and winning might see you get legal fees plus a bit of money back doesn't change the calculus -- the worst case outcome is still prison.
It certainly changes the calculus: it's much easier to get a lawyer willing to work on contingency if there is a financial reward for winning. In civil cases it's quite common for lawyers to work on contingency because so many civil cases are obviously winnable, and have an immediate payout.
Of course, in practice what really would happen is it would be far less common for prosecutors to prosecute people when there isn't a solid case against them. If what I'm suggesting was how criminal cases worked, I doubt that Backpage would have been charged at all.
Note that I also think that plea deals should be much less common, or even totally banned.
