Every enquiry is, to some extent "political", but in a free country with a free press it is very difficult hide the facts - even in wartime.
Reading "between the lines", the truth (or something approaching it) is clear even in the case of Lord Mersey's WWI enquiry. It seems obvious, for example, that the wartime crew were not particularly efficient because many of the best men were in the Navy, and this must have had an impact on their struggle to launch the boats in difficult conditions. Similarly, wartime economies meant that not all of the Lusitania's boilers were in use, and she had thereby lost much of her high-speed advantage.
The vessel was almost certainly carrying war supplies of one kind or another, but I think this was regarded by Lord Mersey as a red herring. The fact is, the Germans had "crossed a line" and escalated the war by sinking a merchant vessel. This was an act of "wilful and wholesale murder" - not my words, not Lord Mersey's words but those of the Kinsale Coroner, a Sinn Fein supporter and no particular friend of the British state.