That build makes no sense to me, mixing fire and phys damage and just gearing for the phys part.
Just use the fire DoT rune and gear for fire% imo. Like
Monk Lashing Tail Kick Build with the Sunwuko set (Patch 2.4.3 / Season 9) or dig up Quin's version from last season on dfans.
I've got the opposite problem. RNGesus decided I needed all the stuff for bells instead of LTK, so now I'm playing that. It's not bad, does TX pretty fast, but it definitely does not scale well compared to LTK. The moment it takes more than 1-2 bells to kill anything other than the RG things slow way down. I don't think I'm going to keep chasing after the LTK gear though; I've got almost everything for a generator build now too and I know that's going to end up being a lot better than either of the Sunwuko builds in the long run.