I think there isn't that much practical difference for volume search between 4 fixed panels and 1 rotating panel.
However, in terms of damage resilience, even minor damage to the rotation mechanism will result in a mission kill.
In comparison, minor damage to part of a fixed panel means the rest of the panel can still operate.
And in a high intensity conflict, there will certainly be battle damage
Plus you have the other 3 AESA panel faces separately located on the rest of the superstructure.
---
Something similar applies to the Sampson rotating fire-control X-Band radar at the top of the Type-45 mast versus say the 4 fixed X-Band panels at the top of the Type-055 mast.
But in addition, what happens when there is a coordinated multi-vector attack? The rotating nature of the Sampson imposes critical update delays
---
Plus from a doctrinal perspective, the British Navy can't rely on AWACs so would benefit from a higher placed radar. In comparison, both the US Navy and Chinese Navy can expect AWACs to provide over the horizon radar coverage.
It also helps that rotating radars are cheaper, as the British military has been operating on shoestring budgets for decades now.
Note that the lack of British carrier AWACs was a budgetary decision.
SAMPSON radar is an S-Band not an X. The Type 45 does not have any X-band air defense radars like the Type 055. The Type 45 has the SAMPSON S-Band radar on top of the mast and the S1850 (Thales) L-band radar.
The Type 055 had has four S-Band fixed radars on the superstructure and four X-Band radars on the top mast.
The L-Band on the Type 45 gives terrific range and better anti stealth detection. However L-band isn't very good against small diameter objects flying very low over the water where it's prone to sea clutter. That's your typical sea skimming missile. Even S-Band has problems with sea clutter.
To deal with sea clutter, you need higher frequency radars that give better resolution. Water doesn't reflect back higher radar frequencies, they tend to absorb it instead so it doesn't reflect back as clutter.
However having both S and X band search radars on the same ship adds to its cost. The USN is acutely aware of the sea skimmer problem by adding the X-Band SPQ-9B radar onto AEGIS destroyers as an upgrade. The Zumwalt was originally planned to have both S and X band AESA radars for this reason. But budgeting issues meant canceling the S-Band radars and leaving the X-Band radars instead. That alone tells you that defending low flyers has become a bigger issue than dealing high altitude bombers at range.
The PLAN is aware of this issue having developed the C-band Type 364 radar for this. The Russians in turn developed the X-Band Pozitiv-M radar which actually ended up in the last two Sovremenny sold to the PLAN and incorporated on the Admiral Grigorovich frigates.
IMO, the X-Band Thales APAR, like used on the Sachsen class frigates is a better idea and a much more direct comparison to the Type 055's top mast X-Band radars. That's more clutter proof and a better fit against low flying sea skimmers.
Going to the Japanese Navy, the Akizuki and Asahi class of destroyers rely on a combination of C and X band, and the Mogami frigates use X-Band exclusively. So there's the trend going for the higher bands.
The 054B relies on a combination of S and X band radars, the X band radar is another dual faced phase array rotating under a dome beneath the ESM array.
