Can only take your word for most of your post.
i recognise the point re yields vs loads. A lot of airports look at loads and load factors and think all is well, but from an airline's perspective, they could be dumping prices in order to fill the planes.
Having some experience within aviation revenue I understand this, but I find the airlines operating highly unlikely to have done this, not least KLM. If they said they were happy with loads and the flights were 'performing well' then yields will not have been so much a problem. The flights operated for longer than the typical 6 month trial seasons.
capitalise on the fact that the Sheffield City Region already includes this 3000m runway and lobby for fast road connections'
That there is a 3000m runway there is irrelevant, what is your point? Are you trying to suggest that the airport could attract long-haul operators? The airport has failed thus far to provide business destinations that are supported sufficiently. It has to be understandable why business groups are becoming impatient, particularly when they had an airport that in their view was perfectly capable of providing what they wanted in a far better location.. Hence, there are people prepared to put £millions into reopening the place.