From inception on CVF/QEC there was always a presumption in favour of STOVL operations, based on the early concepts for a STOVL Strike Fighter or SSF. Even when the programme was Future Carrier Borne Aircraft (FCBA), this was still the preferred option as it was in the comfort zone and many of the "operability vs sea state" and cost of training arguments seemed compelling. The early assumptions were also that STOVL ships would be significantly smaller and therefore much cheaper.
However, risk to a STOVL programme was always acknowledged and so CTOL and STOBAR (even ASTOBAR) ops were looked at, with what was EF2000 and FA18E.
Round about 2000/2001 it became clear that given the proposed sortie rate and deck parking requirements, there would actually eb little difference in size between STOVL and CTOL options (the STOBAR ones were larger) and so the "adaptable" carrier idea was born to try and balance the risk to the aircraft programme.
It is also important to understand what is meant by "adaptable". It is not (and never has been) the equivalent of Fit To Receive or Fitted For But Not With. It was simply arranging the flightdeck and gallery deck areas such that area and volume for two cats and an angled deck were available and that sufficient weight margin was available to accommodate these systems.
The arresting element is fairly straightforward. Mk7 Mod 4 is a relative self-contained simple system, no major dramas there. The real issue was always about the cats and unfortunately the timing was simply all wrong. EMALS was always the preferred option, but was so immature at the time that it added a lot of risk. Using steam was also risky in terms of through-life cost and people, so you ended up with two different factors militating against CTOL, whatever the "benefits" of the operating mode.
It was only when the payload and cancellation risks of F35B got really serious taht people really started taking the CTOL option seriously IMO.