Hero of Tython is actually immensely powerful in the ways of the Force. He was noted to possess "Jedi Master like abilities" when he was just a padawan; by the end of his story arc, he could be as good as Luke.
HoT once forced a "gigantic laser bridge" to close without even a gesture when an army of droids was walking through it to reach his position, causing the army to fall between the peaks. In addition, he have feats of collapsing portions of structures and vice versa much earlier in his story arc.
Problem with HoT is that he is not much explored in the ways of the Force in canon. However, he is extremely good in Jedi arts.
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And yes, First Son is apparently among the most powerful Force-users of all times; among the (very) elite.