I don't think either of us engineers ever suggested dual thrust loss is somehow fine
Uhh, except you kind of did....operative words in bold.
Further, although ICI caused some temporary thrust losses and engine damage, there were no shutdowns,
"Although" "Some" "Temporary".
Lots of hedging in that statement but hey, ok! There were no engine shutdowns, it's all good.
The only dual engine thrust loss that I recall happened on a Boeing 767 out of LA when the pilots on the pointy end accidentally shut off the fuel flow to the engines.
It was a Pratt JT9D powered B767-200 (not a particularly fine engine BTW. I operated this engine on both the B767 and B747 Classic) that suffered an engine surge right after takeoff. The crew followed the drill and went to select the EECs off. Unfortunately, the EEC switches were located down next to the fuel control cutoff switches, and they mistakenly switched the fuel control switches off instead of the EECs. Fortunately they quickly realized their error and the engines relit almost instantly. Part of the cause was attributed to poor ergonomics, IE: placing secondary engine control switches (EEC switches) next to primary engine control switches (fuel control switches). As you both probably know, the EEC switches were subsequently relocated to the overhead panel. The other three dual engine failures that come to mind (Air Canada, Air Mauritius and Air Transat) were caused by fuel starvation, not engine failure due to the issues we're seeing on the GenX and Trents. But again, you are rather making my point for me; when we can look at four dual thrust failures over a period of about 36 years and realize that not one of them was attributable to poor design/poorly understood phenomena/premature wear/etc, this new generation of large turbofan engines compares poorly to the first generation of P&W and GE engines.
So how do you test for something that isn't clearly understood and can't be reproduced like normal certification ice testing is done?
The answer is that you
cannot certify
until the problem is
completely understood and associated risks mitigated. The JT9 and CF6 were well understood engines with perhaps hundreds of thousands of flight hours on them before they were hung on a big twin, the A300. And it was at least another 13 or 14 years until these engines fell under further scrutiny with the advent of ETOPS rules. While ice crystal icing is an elusive and a not well understood phenomena, the industry has been aware of it since approximately 2010. The solution is not an "Oh well, we've known about it for a while but don't understand it completely, but let's go ahead and certify anyway. We'll see what happens". Your collective attitude is reminiscent of the Challenger Disaster - IE: "We don't know enough about the behaviour of the O-rings in subzero weather but nothing has ever happened before so let's launch anyway". We all know how that turned out and the resulting investigation led Professor Diane Vaughan to say:
"Social normalization of deviance means that people within the organization become so much accustomed to a deviant behavior that they don't consider it as deviant, despite the fact that they far exceed their own rules for the elementary safety"
If we can agree that the first generation large high-bypass turbofan engines were superb, then to me it is normalizing deviance to suggest that these new engines are really, really good too. Particularly when the evidence points the other way. At the peak, there were approximately 50 Trent 787s grounded, and on the other engine we had to learn the hard way, as a result of the ANA incident, that we have to do engine runups to shed ice just like in the propeller days. At least, post-incidents, the right thing was done and aircraft were grounded. Had this have been done after the American Airlines cargo door blowout in 1972, perhaps 346 people on a Turkish Airlines DC10 wouldn't have died two years later.
The real shame of it though, is that the industry has to keep relearning lessons already learned. Below is a short summary (not written by me) of an incident from author Ernest K. Gann's flying career as detailed in his book: "The High And The Mighty".
Another interesting story to prove this point also almost cost Ernie his life. He was flying a DC-4 after the war for an airline. Ernie considered the DC-4 a very safe and reliable aircraft.
After takeoff on a flight from San Francisco to Honolulu, as the aircraft ascended above 3,000 feet, all four big radials began acting up, with at least one of the engines quitting entirely. Had the crew not taken immediate action to adjust throttles, mixtures, and prop pitch, all four engines likely would have stopped turning.
The mystery of the reluctant engines was solved after they nursed the aircraft back to San Francisco. Prior to the flight, unknown to the flight crew, the spark plugs had been replaced with a “new and improved” version for this model of Pratt & Whitney engines. The new engine/spark plug combination had never been field tested, but the Pratt & Whitney engineers had assured their higher-ups that their slide rules confirmed the plugs would work. The plugs did not; at least not above 3,000 feet. Had Ernie viewed the engine log books or made some inquiries about the nature of the maintenance performed on the aircraft, he may have been in a better position to evaluate the real flight risk on the ramp rather than being forced to deal with it in-flight.