Good for you, I guess?

I'm not saying there aren't outliers or people in CO who only own a tri bike. Perhaps if you have DI2 on the brake levers things are different, but for the majority who have mechanical shifting, a Tri bike is not a great climbing bike, given the need for frequent switching of gears out of aero, and trying to climb in aero at 10-12MPH (or slower if a super steep climb) is pretty unstable and you can't pull against the aerobars nearly as well as you can on shift levers on a road bike. It's like trying to take Prius on backcountry trail roads. It might make it, but it's not the best tool for the job. Not to mention a lot of local group rides won't allow tri-bikes for safety reasons.

Again, bike fitness is transferable. As long as you're comfortable on your tri bike and have done enough practice rides, it's not as if training on your road bike is going to take away from your Tri bike fitness. Look at the UCI world championship TT. The top guys are almost always top tier Tour guys who... you guessed it, spend most of their time training on road bikes. Looking down on someone because they train a bulk of their miles on a road bike is pretty stupid in my opinion, assuming they have a well-fitting Tri bike and do ride on occasion to get a comfortable position. If it's good enough for the pros, it's good enough for the rest of the people.