F-35's radar is mind blowing, with 'yuge' growth already planned. Sensors, likewise. Fusion IS working very well but still being improved (and will continue to develop through-life); missiles are.....well, very nice indeed. Holds its own against F-16 very well -but remember it isn't a lightweight-class fighter. Considering the design challenges, the STOVL variant is a credit to ingenuity - there isn't another fighter in the world able to fly at Max AUW from a 1500ft strip - or 600ft ramped deck - dash to M1.6 return and land at zero forward airspeed. Oh, and you won't get a radar lock on the old girl either.
Yeah, I'd buy 138 for the UK as well. The high cost is also the price of being relevant in the air for the next 40 years. Obsolescence will see F-15, 16, 18 in the boneyard soon enough.