I agree! It's the nature of the beast that this type of failure will happen with this technology and volumes this size. We're working hard to minimize it and make fixing it as small of a pain as possible for the unlucky few that have to deal with it.
Then, even though I am not a Keysight customer, and despite that I think that being present in a forum like this is great, I am going to make a brutally honest but constructive criticism: that naivety by your designers is simply unacceptable.
If the flash is so error prone it wouldn't harm anyone to make it easily replaceable. And, for situations such as this, it's mandatory to have a bare minimum boot environment in ROM so that at least you can replace a broken firmware. Accidents happen. A power outage can bite you during an update. Firmware can be corrupted for whatever reason, even "Alpha particle impact", as Cisco uses to call it. There are countless ways in which it can go wrong. With an adequate recovery mechanism, the customer will at most call technical support or even look up a support web page. What happens when that option is not available? Headaches, lost time and even money (seems, even though this seems to be a misunderstanding).
Last year I suffered one of those episodes with an expensive Firewire audio interface (Metric Halo). Suddenly something was badly corrupted and it refused to boot. After an email to the technical support they gave me a procedure that worked without faults. It booted into an old version of the firmware
in ROM, and I could install the latest version without problems.
I know that many of the customers of high end equipment are used to support contracts but a refusal to boot without a proper recovery mechanism is plain simply bad design. Not intending to be nasty, but I didn't expect that from a high end manufacturer. And I'm sure that if I tell this story to a friend who worked in Santa Rosa several years ago he won't believe it.
Anyway, take it as a constructive criticism. Never underestimate the value of a boot loader in ROM including a firmware update mechanism, together with some firmware image validation. And, plese, for God's sake, do not take the awful PC firmware as an example. It's hard to do worse!