The rationale is perfectly logical
...
The MoD rationale for Crowsnest OSD 2030 is perfectly logical.
Based on the Merlin's recently extended service life to 2040, they're now anticipating a shortage of HM2 airframes after 2030, They have also just learned (thanks ZH844) that the 'Orphan 8 HM1s' at Gosport are too far gone to be of any practical use (sound familiar ?)
The first problem with Crowsnest is that it is an operational either/or choice on the day, complicated by the limited number of CN capable airframes. Having to decide which way to swing is clearly a serious distraction if you're 'unlucky enough' to be faced with simultaneous subsurface and air threats for an extended period of time.
There just aren't enough available HM2 airframes even now, to realistically fulfil both AEW and ASW tasks from a single Carrier and at the same time equip even the few available escorts and ancillary ships that expect to carry Merlin. Not forgetting training, deep maintenance and reserve requirements. And that's a plan that's now got to work until 2040.
Given that the choice of radar for Crowsnest arguably put it out of date even before IOC - expecting it to be still viable after 2030 would be hard to spin, even for MoD.
OTOH - These problems are easily solved at a stroke by -
1. Taking Crowsnest out of service in 2030, which releases 10 or so airframes for ASW.
2. Selecting a suitable carrier-based UAV with modern AEW radar, and making IOC no later than 2030, thus avoiding a boring capability gap.
When it's all gone TU and PT in 2029, the architects of this master strategy will be long gone (to the Lords etc) and will calling for someone to be held to account.
What's not to like ?
LFH
If it ain't AESA - it ain't gonna win.