Well, I did ask for someone to point out what I was missing, and this is a sort of apology to Garmin for my harsh words. It took a friendly Garmin Level 2 support person named Brad to contact me and engage in a technical conversation, which included screenshots from my device and a discussion of what the documentation actually meant, to determine that I was confused by what Garmin calls Guide Text appearing in separate navigation-related popups that Brad called “Intersectional Popups”; I’m pretty sure that’s not official terminology, and I’m unsure if the artefacts are actually named officially.
Guide Text is actually limited to the map screen, but not definitively stated as such in the documentation, only as “turn-by-turn navigation prompts” (although it is in a Map Settings section). As stated previously, it’s entirely reasonable to think that popup text that tells you where to navigate meets that description, but careful examination of the device settings shows that the same text appears in two separate ways, and one works as the device menu prescribes while the other doesn’t.
Brad said that the Edge 1000 works more sensibly with respect to courses, and that there is apparently new firmware to come out for the 810 that makes it work better. Here’s hoping.
I think that Garmin documentation is poor, and I wish that Level 1 support actually understood the devices they purport to help you with. I also wish the escalation procedures were better – if Level 1 had actually passed my concern up the chain 6 months ago when I first started questioning their knowledge of the device, this would have been sorted much less acrimoniously.
At any rate, I now own an Edge 1000 and am much happier.