There are many factors that go into pleading guilty and being sentenced. It is complicated and a defendant should have the best legal council to explore all mitigating factors. Nothing is cut and dry. Hire the best you can afford. Good luck.
If you were charged with 1st degree murder, special circumstances, 16 years would be a great offer. However in my experience it is rare that I would recommend that my client take such a high offer in almost any other kind of case. In some counties the DA offers ridiculously high offers and then doubles or triples them if you don't accept. So yes a good lawyer who knows the county where this person is being prosecuted may be able to get the offer reduced. It all depends on the facts of the case which shouldn't be set forth here.
Yes. There is a huge difference between being factually guilty (what I believe you call "caught red-handed") and being legally guilty. A skilled lawyer know how to expose that difference to win a case or use as leverage to get a better deal.