Hi Stuart. If I was comparing "dive computers only" then the Teric would not even be in the running. It would be either the Perdix AI or the Scubapro G2. For precisely the reason you mentioned--large displays and ease of viewing (yes, I have "older eyes"). And, if I wanted only a dive-dedicated device, it would be one of those and not the Garmin. I don't really care for "watch size" in a dive computer.
It is the attractiveness of the Garmin as a multi-feature device (I regularly do the things I mentioned above) that tips the balance. As for "inactive" people, are they putting a lot of money into diving? Sure, it is not going to be worth it to them if their only sport is diving. As for cost, I suppose I could get a Perdix AI with transmitter for about $1285 (DGX price). Garmin with transmitter is 1900. So, a cost difference of $615. Garmin fenix 6s is 799 and is basically everything the Descent is, except for the diving capabilities. So, that and the Perdix would total 2,085--not much more. But, you do lose a few things (GPS logging of shore or boat dive entry/exit points, InReach integration with the Descent as a dive safety feature, integrating my activity while diving into my daily health data). I am more inclined to save a little and have everything rolled into one device and I certainly wouldn't mind wearing it as my daily watch. I don't drag through wrecks/caves or grapple with lobsters under reefs. I hang in the water, run my scooter, take photos and generally stay off the bottom. So the potential for scratching/dinging the watch is less of a concern for me. But I can see where some folks might want a dive computer to trash that is not their daily watch.
As for whether the Garmin or Teric is easiest or more intuitive, I have only had shop time with them, not dive time. But, it seems pretty clear that the Garmin's display organization will be more useful and easier to understand than the Teric's during the dive, mainly due to its customizability. On the Garmin, you can put heading or temp on the top in "small" unobtrusive font but still readable and useful. Next line is larger font for "gas" info and will show pressure and GTR. Third line is "Deco Info" and displays NDL and depth in the largest font. Bottom is small font and shows dive time. The four most important life-safety items for any dive (pressure, GTR, NDL, depth) are large and front-and center. The second-level important info (time) is also shown but less obtrusive. One tap and you are in the excellent compass screen, much bigger and more useful that Teric and also shows depth and NDL (I did not have time to see if you could add pressure to that screen as well).
Teric is just not as well laid out. Depth is huge. Time is huge--not necessary. The actual key life-safety information--NDL and tank pressure--are tiny and in the middle. Not good. Compass comes up in the middle row and hides NDL and tank pressure. Or, you have to go to a tiny font layout to see both the compass and NDL/Pressure at the same time. Either way, not good. The "huge" numbers should be depth and NDL with time and pressure on the middle row, Or, depth and pressure huge with time and NDL on the middle row, but you cannot set either of these up as a custom display.
The Teric seduces with is beauty. Bright, crisp, colorful, the compass flows like water--just a joy to look at (but not in sunlight!). But, for giving me the critical stuff "at a glance" without having to "look for" the info in the small fonts--the Garmin will win.