Excellent point about having a garage (hanger space) so could we simply have the Illustrious carry both?
Illustrious is a far better option than the Ark... That ship will need a very expensive refit to get her to a similar operational standard and would we need both ships or could Illustrious deploy land forces as well as fixed wing?
HMS Centaur embarked an extra helicopter squadron plus 45 Cdo Royal Marines to help subdue a mutiny... I am only saying this to highlight how a fixed wing carrier can be adapted to carry out more than one role.
As usual I am in full agreement with Not-a-Boffin and experience shows that a surface ship alone is not capable of offering total air cover. Hopefully we have learned valuable lessons from our last major conflict and we needed air power... we needed ships to carry that air power.