George (and others),
Sorry if I'm repeating myself here but....
The F-35B's vertical landing performance was not, and is not, 'deficient'. It meets the KPP set down in the user's requirement, and it was a Key Performance Parameter because VL performance was a driver of the design. (The existence of this KPP was a main driver for the redesign for the aircraft after 2003 when LM allowed the weight of all three variants to get out of control).
The UK signed up to the original requirement, which used a US Mil Spec definition of a 'tropical day'. Later on (around 2003) the UK came back and asked if the VL performance could be maintained at even hotter temperatures and lower densities (this set of conditions were called the 'UK Hot Day' and reflected conditions they had experienced in the Northern Gulf in preceding years).
LM did a short study and examined the potential of an SRVL. Initial assessments showed that these could deliver a serious amount of additional 'bring back' on a 'UK Hot Day', and things moved on from there. Progress was stopped when the UK switched to cat and trap in 2010, and had to be restarted in 2012, when they changed back to STOVL. The recent articles show how far they've come, including the development of the novel 'Bedford Array' landing lights aid. The F-35B's very advanced flight controls help to deliver low workload SRVLs, but as Wizzer points out, wet or slippery decks have to be considered. Normal carrier borne stuff.
So to summarise - the UK asked for more performance over the original requirement, and the SRVL has been adopted as the way to achieve it. It's called getting as much out off the aircraft as you can. Hope this helps.
Best Regards as ever to all those developing new ways to do carrier borne aviation,
Engines