As of 16/10/2020, the Krokul Mining Pick is not working in Legion areas.
I have tried mining in Val’sharah (both having the pick equipped and in inventory) and the casting time was 3.2s (instead of 1.7s as it should be).
Also tried mining in Highmountain with the same results: the mining pick does nothing to shorten the casting time.
Bugs are reported ingame and if you look at the link you supply you will see others are having the same problem.
Will definitely try the in-game report.
Regarding the comments from others that you mention, the last one was from 2018, and the mining pick was working well before 9.0.1, so I doubt it is the same problem.