The cool thing about hints is you can quickly drop in a hint to confirm your suspicions and narrow down the problem, rather than trying to do this sort of diagnosis in a vacuum. But because some people use hints for evil, nobody is allowed to use them.
Access method is just part of the story. Same index may be accessed in different ways, you might also want to combine them. Sometimes you may change table join order to see how it estimates (or executes). Usually there are two parts 1) cost and reasoning for some estimation 2) how it executes (timings, resource usage, locks/contention)
