We should also remember that with each rebirth you get stronger and the breakthrough from mortal to houtian double our stats iirc, so there is a possibillity an EX wu heir can have the strength of a weak MX and a MX wu heir equivilant to an average LX , this all about stats ofc, adding the golden seed and the dao makes Wu heir even stronger, so this is purely from a stats POVOverpowering a E-X to M-X level Art seems pretty good as a feat for me, all this without manuals or even forming a foundation. After reaching Qi-Sea and preparing our foundation I wouldn't be surprised with Wu Heir being able to fight and defeat Shangtian's/CF's even.
Imagine we become what ruo is to us to xiantian
Peak X strength at L X