if we were ever in the position of finding ourselves in, or about to be in, a conflict that was considered to be so vital to the national interest that we need to send both carriers - and therefore pretty much every servicable F-35 and qualified pilot we had - i rather hope that every single asset that was capable of being sent would be.
personally i don't really care about piracy off the Horn of Africa, or the Gulf - or indeed COIN conflicts in sub-Saharan Africa or wherethe****istan, so i don't care about stripping them of a T45 in order to protect the carriers. if we need to watch the North sea, or secure Cyprus or the FI we just ramp up the Typhoon force - which will do just as good a job as a T45...
a QE with 30 F-35 and 2 T45 can look after itself far more comprehensively than a 30k Invincible 2.0 with 15 F-35 and 3 T45 - a battlegroup with 2 QE's and 60 F-35 and 2 or 3 T45 is going to be somewhere between a bloody hard target and invunerable...