If you want to do penetration missions, even with the F-35, you need AEW/Elint/Data-comms relay to go with you - a rotary MASC cannot do that and would seem totally illogical for the stated roles of the CVF/F-35 wing.
If only fleet defence is required, why not save money and go for a
ship based blimp solution? It provides a 24 hour coverage solution without taking up the deck space. I would suggest the radar signature of a JLENS, with it's slow speed to hide in the MTI notch, is comparable or less than that of an on-task helo.
Or even go the whole hog and have a naval dirigible which can operate detached from the carrier but still do long-line refuelling and resupply.
But, as you say, not built in Yeovil....