Upon investigation, only Mr. Liang, the Elder, is the most suitable.
On the other hand, the Grand Secretary's control over the Ministry of Revenue is no longer as strong as before, partly because Minister Wang has pledged allegiance to Prince Yu.
Speaking of which, Minister Wang's rise to his position was supported by the Grand Secretary, only to be backstabbed so quickly.
But looking from Minister Wang's perspective, an overly powerful Grand Secretary is bound to be checked and balanced. If he doesn't turn against him, others will. Better to seize the power himself.
After all, he's just grabbing power, not sabotaging the reform.