CJ
I think we have to distinguish between the basic aircraft, which is superb, and equipment. The original radar had a 28 degree blind arc and, as you say, was acceptable for ASW. This imitation was understood and at the first opportunity, only a few years after Mk1 ISD, a development contract was let which resulted in a 14 degree blind arc (approx) and much higher power. (The spec was written by RRE).
In this period, the RAF took delivery of the Mk3 and retained the old RN radar with the large blind arc/low power. When they had the Mk3A approved, in about 1993, the RN were getting shot of the newer radar as Merlin was due, and offered the RAF sufficient scanners, transmitters etc to upgrade. Not quite free of charge, but a lot cheaper than what they did, which was get a digital processor and colour display, which left them with a hybrid which was neither here nor there.
Part of the problem here was that even into the mid-90s the RAF's radar maintenance policy was 1A, 2BC at RNARW Copenacre, 3BCD at Fleetlands. The problem was RNARW had closed in about 1983 (!) and the entire 2/3 line burden fell to Fleetlands. But, as the RN had replaced this radar, Fleetlands' capacity had been chopped by 80% (as 80% of aircraft now had the new radar).
Allied to this, RN observers were trained on the RNGT, a raw radar. They expected noise paint on the screen. But many RAF observers were trained on the BPRT, and in 1989 we had the ludicrous situation whereby, despite having inherited 140 old radars from the RN, the RAF didn't have enough serviceable out of a stock of 180 to fit a 20 aircraft Mk3 fleet. Well over 100 complete radars were "awaiting final test" at Fleetlands at any one time. Poor or non-existent training meant the operators were rejecting them for "noise", as they expected clean "digital" displays. There was a 99% No Fault Found Rate at Fleetlands, but the test bottleneck meant a backlog. In one 3 month period around this time, every single Sea King Mk3 had a complete radar change, every day. Not one of them was u/s. That was a far bigger problem to MoD than the blind arc.
I remember us going to Finningley to suss the problem. My oppo (best radar diag in the MoD) was standing next to the radar instructor in the aircraft on the pan. We could see the nearby church spire, but little else. He said, if with go up to 1000', that's still all we'll see. My mate reached across and tweaked Swept Gain and the screen lit up. "FFS, we're not allowed to touch these controls". Yes you are, the ones you can't touch are under this screwed down flap. Two days later we delivered a full training rig and documentation. And we dropped £80 in the mess bandit.
The German version (Mk42 I think) overcame this by having both nose and dorsal radomes, but this was a different radar.