To be fair, the ignorance is not entirely unjustified. No one knew wtf was causing it or how to fix it. At least the dealer (if not Triumph themselves!) were acknowledging the seriousness of the issue, and attempting to put it right for me.
I'm really pleased yours has been all good since the work has been done, but given that you never had much of a problem beforehand, it might not prove very much. How long have you had the bike, and roughly how many miles have you done? I'm guessing not much (like myself) given covid and lockdowns. I've had mine over a year now, but only managed about 1500 miles. In that time it's been in for bleeding of the brakes I think 3 times (one of which was the replacement of the brake fluid, at their suggestion). So since I was one of the first to get a Rocket, collecting it (the TFC) in mid Jan 2020, this is probably partly why I've had it fail so many times, and why the dealer was happy to attempt changing the fluid.
What's has been especially interesting for me, is that before we got about 3 months of continuous rain starting early November, I had ridden the bike, and found that the rear brake was once again getting rather ineffective - not terrible, but not good. I went to ride the bike again for the first time since then at the weekend, and the rear brake is now entirely gone. Nothing at all. You could happily stand off the bike, keep your foot on the rear brake pressed all the way down, and just push it around. What's interesting about this to me, is that it means the deterioration is not a function of heat from the engine (as some thought it might be), it's not a function of miles ridden, or amount of brake use, it seems to literally just be a deterioration over time.
Anyway, after originally posting here, I did find the above procedure details you mention. As I've said I'm no tech, I don't know what steps are involved in the other work they've already done, but I'd half-expect that to change the brake fluid, you'd need to purge the ABS system. Having said that, they never did specifically mention trying anything with the ABS, so here's hoping that that is the problem, and that this procedure is the silver bullet. Because aside from the dodgy rear brakes, I absolutely LOVE this bike!