F35 is some years off, as are the carriers, even if it can even take off. Wars don't wait on procurement and the Yanks don't get involved in all the wars we fight....err, they were 2 years late the last time we asked for their help!
Rapier has a well-known difficulty with targets above a certain height and beyond a certain range! You can trust your air defence to HVM if you wish, but I wouldn't recommend it!
The point of air defence is it is meant to be layered! T42 on picket with jets (with sensors please, not GR9!) and something (Sea King) for beyond visual range coverage all up-threat. The threat doesn't have to actually be a threat to cause massive damage - a visual ID before a shootdown may prevent a USS Vincennes-type incident. But if you had no sensor you would feel very vulnerable! And NEC is only any good if there are sensors to plug into the network, a lesson that many have had difficulty grasping - nothing in, nothing out as the picture doesn't just come from nowhere!
There are many problems!!! Too much jam tomorrow (next week) and the cupboard is always empty at the wrong time.