First consider that the MAA is rather dependant on DE&S informing them (and the DH) of the problems with any particular fleet.
Do you think the PT's are minded to forward any particular damning document to the DH or MAA?
At the moment my view of the MAA is mainly positive. But has the DE&S that H-C rightly criticised been minded to change and to actual reveal the risks that have been buried for many years?
The MAA has direct access to other sources for such information, should they dare to “go there”; not least the raft of ART reports and direct access to Design Authorities and Custodians. They should be conducting their own independent assessment and comparing it with what the PTs offer them. Any discrepancy should be followed up.
They will not go there, because the ART reports (by the Inspector of Flight Safety) reveal the lie that is the H-C report, when he claimed the failings only commenced in 1998. The CHART report of August 1992 alone exposes this lie. (So when did the RAF stop using captured Argentinian pubs to maintain Chinook?)
Alcock and Graydon claimed that CHART had nothing to do with Chinook Mk2, yet it mentioned Mk2 383 (!!!) times. Dr Fox repeated this lie, which amply demonstrates who briefs him and how he was misled. The lie has been pointed out to the MAA, who refuse to comment; an abrogation unworthy of any "Authority".
You are correct in that PTs will withhold and mislead. For a start, they refuse to answer the above question. In one particular case, Sea King AsaC, they even deny an investigation took place and a report published, which requires a certain confidence (misplaced!) that all the evidence has been destroyed.
What is the MAA doing about this? Nothing.
Finally, did H-C criticise DE&S? He actually criticised DLO (Baber and Eagles from the IPT, and Cowan and Pledger as CDL) and that criticism has been revealed as utterly vindictive and designed to protect VSOs. To get to the truth, follow the lies. Who lied? (See above).