I couldn’t tell you the specific apps but I’m presuming it’s the dialler, clock, calendar, weather?
I've owned HTC 10, and it was a fantastic device. Build quality superior by far even to something like iPhone or Samsung S/Note. Only real issue was lousy wi-fi signal, and that was the reason I ditched the device. But till this day, that was the best phone to hold in hand. A real 'man' phone, heavy, metal, and buttons were really great to push! (hard to describe it, but they had great feel to them).
Everything expect really lousy wi-fi signal was great. Especially software.
Now, that was the first device that they pushed without their own apps (email, browser, etc.).
Now, don't take my word for it, I really can't remember that far in the past (hic!), especially because I've owned that device about a month or so, but they didn't have a dedicated calendar app, or clock, or weather app.
Only dedicated app that they really had was HTC dialer. And I do hope that they still have it, because HTC always had the best dialer ever, on all phones, any OS.
Their dialer was 'smart'. Lets say I have a person named 'John Smith' in my contacts, and some more Johns also. If I type Joh + S, it would recognise it right away. Something Samsung dialler still doesn't support. And If I had multiple 'Johns', without surname, but I would occasionally call one John more then others, HTC dialler would remember that, and put that John in first place.
If I were in charge in Google, I would either copy/paste HTC dialler into stock Android, or just purchase that part from HTC.
So I believe you are mistaken. HTC ditched their apps, everything except dialler (can't speak for phone later then HTC 10 though), and rightly so! I would install their dialler on every phone out there. Especially iphone