My understanding (according to those within football) is a successful transfer policy is a strike rate of 1 in 3?

To decide what is successful we then need to decide how we are judging success. Are we looking at players to take us up the leagues immediately (as you are) or are we looking at players who could be viewed as an investment over the long-term.

Traore, Jarvis, Hinchy and Grant are all firmly in the investment category, the success of these transfers can only be properly judged over the longer term. We need to be patient with them. Most footballers don't peak until their mid to late 20's, there plenty of potential improvement in these 4, plus Traore is trying to settle in a different country.

What the transfer policy has done well is when speculating on players it is important we don't get saddled with their wages long-term if it doesn't work out. In that regard Brown, Martin and Whittaker aren't shockers and can be viewed as a long term trial.