I think I got your point. I just approached the problem from the other side. I think limiting a prosecutor's ability to bargain would be easier from a legislative standpoint than getting involved in sentencing, and more effective since the sentence asked by the prosecution is really just a recommendation. Either way, the important part is ratio of sentence to plea bargain, if I understood you correctly.
Prosecutors will go for very low plea bargains if their case is shaky, with huge penalties for not accepting the plea, so many shaky cases never make it to trial. By reversing the situation you end up with half of the maximum rather than maybe 10% of it, in effect most plea offers would increase rather than stay at their current level and many more cases would have to be tried.
I think that the idea here is to prevent prosecutors from charging people when they only have a really shaky case then using the leverage of a small plea to force people into pleading guilty. If prosecutors don't want to lose cases, and they can't force people to accept really low pleas then they would have to stop trying to get people on really shaky cases.
Well that is the whole point - if the case is shaky (i.e., the accused is likely to be innocent), then the case should be either dropped or go to trial.
Any system that results in accepted guilty pleas for such cases is broken and evil, and should be destroyed.
