When a person davens by a person’s kever he is still davening directly to Hashem-from his heart-just at a holy location but when a person goes to a Rebbe to daven for him, he makes a major drop in Faith in Hashem by turning his dependence on another human being when he really should be going DIRECTLY to Hashem from his heart for help.
Do we now see the real difference between going straight to Hashem from your heart versus going to a middleman shliach and asking him to daven for you?
Sure he’s a big tzaddik and Hashem could say I don’t want to n the tzaddik so let me answer his tefillos…. But at the end of the day person going DIRECTLY to Hashem from your heart still has a bigger chance of his tefillos getting answered then going through a middleman
Start working on your direct relationship with Hashem today and build it up as you get closer and closer to Hashem