Not everybody can train on their Tri bike. I live in CO. The only place near me that is pancake flat is a multi-use bike path and a ~2 mile stretch of a state park where I do workouts at. Otherwise, my "flat" rides have over 700' of elevation gain, with an average ride of 1400-1800'. Some of my longer rides have well over 3k in elevation gain.

Only 1 ride of mine per week is on my Tri bike -- my workout day where I do a number of 4-mile out and back intervals on that state park road. The rest of my rides are on my road bike. Climbing on a Tri bike sucks. Overall cycling fitness is similar between your Tri and Road bikes. Pushing 220W for 30 minutes up a mountain at 11MPH and 90RPM is going to be a similar effort to pushing 220W for 30 minutes at 90RPM on a long flat stretch of road at 23MPH.

Also, it's going to be location dependent. Back in IL, quite a few triathletes I know only had a Tri bike. Or a Tri bike and a beater road bike. So it's no wonder they're going to spend the most time training on a Tri bike, because it's their best/only bike. At the same time, I look back to some of my rides in IL and I'm only at 100-200' of elevation gain over 20-30 miles.

Of the 5 triathletes I'm personally friends with here in CO, 4 have nice road bikes in addition to their Tri bike, and one just uses their road bike with clip-ons for races.

As far as the bike in question - no doubt it's nice. But it's not necessarily worth spending the $$$$ on this just to get disc brakes.