Noderaser. you've hit on the 'grounds up or down' argument regarding fuses vs. circuit breakers.
All I can say is that I've seen very few over-size breakers, while over-fusing seems to be the norm. Plus, I've never had to try to buy a replacement breaker at 8PM Sunday evening.
(Well, almost never. I did get a service call where the 100-amp breaker feeding a subpanel failed at a laundromat- and that was at 11PM Sunday
As for troubleshooting skills- in all honesty, I'm not impressed by my own. I'm even less impressed by folks whose first assumption is that the breaker is 'weak' or the GFCI 'defective.'