First, there's serious legal doubt about PAGC's authority to kick out the ombudsman and assume the investigation. Maybe a parallel inquiry, not a takeover, as in: Ombudsman, give us all the papers, drop what you're doing, we'll do it.
The ombudsman has first and exclusive jurisdiction over cases recognizable by Sandiganbayan, such as the lamps purchase. It can snatch a graft case from another probe Agency, they don't snatch a graft case from it.
Authority limited
Besides, PAGC authority is limited to administrative complaints against presidential appointees in the executive branch, or those occupying the position of assistant regional director or higher.
Why turn over the lamps case to PAGC which doesn't have jurisdiction over local officials who may be linked to the plunder and which has no authority over its criminal aspect?
Other than dubious legal authority, there's PAGC's lack of credibility.
PAGC was created by executive order (EO 12 of 2001, as amended by EO 327 of 2004). Its umbilical cord is kept at the Palace. PAGC cannot claim substantial independence, especially from a President that still struggles against opposition's stubborn attempts to oust her.
Suspicion of motive
Suspicion of political motive cannot be avoided. PAGC's takeover will effectively scuttle publicity which must be hurting senatorial and local candidates of the ruling party.
The probe will be finished in three months, did they say? Enough time for elections to pass without being influenced by voters' knowledge of the massive stealing.
A full-blown discussion of the case, with the right of suspects to explain, will help educate voters on the choice of government leaders in May.