We often hear this advice given but I'm sorry I just don't buy it. Strength of the autopilot *does* matter. For example I have an undersized wheel pilot on my boat - it simply doesn't have the rated strength for certain conditions, particularly closed-spaced following waves. No amount of sail trim will enable it to do its job. The waves are what are pushing the boat. It depends on the boat design too - a full keeler might track like a train running downwind but a fin keel boat doesn't.
Also the advice that the tiller should be finger light and require no more strength than a 2 year old could muster. They were in high winds with huge close spaced waves from high current interactions. I don't see how you could have finger-light 2-year-old steering in those conditions, even going upwind. The advice to crack off (fall off) a few degrees is good though, as that might have dealt with the waves better. But an underpowered autopilot could still have difficulty even after that.
Sorry, I was away for a bit. What I want is for you to imagine that you had absolutely perfect sail trim at every second. You would find that you could steer the boat quite well with just the sails
alone. This is something they teach young sailors as a way to understand just how little effort should be required to steer. So you should first work
towards improving sail trim before looking at anything else.
Now obviously this is not possible in the real world where winds shift and waves slap at the boat. But what I was trying to impart was that in a perfect world, it shouldn't require more strength than a 2 year old to steer. This is the best and fastest way to sail your boat.
What is vastly more important than the "strength" of your autopilot or the "over time", is the intelligence of the autopilot and it's ability to adapt to the wind wave conditions. They are making APs better all the time and they are really getting towards this goal. Think of the current
that is circling the globe. The autopilot is not so huge that it could overpower that boat when it wants to broach. Rather, that autopilot is so smart that it anticipates and corrects for the broach before it even happens. Even on my own little Olson 30 my autopilot can't overcome when I'm trimmed badly. But is manages the boat nicely when I've got things set correctly. Keep going back to the two year old with his hand on the tiller to get the idea.