I largely agree with you though some sentence reduction for making the court's life easier, avoiding the cost (emotional, time and financial) to witnesses (including the victim) is appropriate it is a question of the magnitude. 10x sentence difference is undue pressure that is enough to make the innocent plead guilty (or worse). An expectation of 30%-50% sentence for pleading early is a significant reduction but not in most cases enough to make an innocent person plead guilty unless it crosses a threshold that allows a suspended sentence or community punishment (in which case the magnitude of any improper conviction is relatively low).

I'm in the UK were there is talk of cautiously introducing some form of plea bargaining. At the moment I think pleading guilty (and how early it is done) is just something taken into by the judge. There may be some deals on the charges brought when there is some discretion but I don't think the opportunities are that great.