I guess I might aswell start with some (partially lesser known) applications that I've found useful since I bought my 2018 MBP:
Pixelmator Pro. I'm not a professional photo editor or anything, but I use the app on a regular basis for some quick but slightly more advanced image edits or drawing some sketches, and I find the app's TB support extraordinarily well done. It puts the entire tool selection bar along with many individual sub-options and controls onto the Touch Bar.
The thing is, many of these tools just don't have a keyboard shortcut because they aren't suitable for one, and this is one aspect that the people arguing against the Touch Bar often deliberately ignore. Want to change the width of your current brush to a value between 1 and 1000? Or want to select one of several dozen different brush types? How do you want to replicate that stuff with KB shortcuts, do you want to assign each individual value between 1 and 1000 a unique keyboard shortcut?
Having a slider or quick-picker for these things on the Touch Bar is actually really convenient because you can leave your mouse cursor wherever it currently is within an image. Want to, say, find the perfect width for a brush to draw a certain line on your image? Without the Touch Bar, you must check the current width of your tool within the image, then move your cursor from there to the on-screen slider to pick a new value, then move the brush back to the image to see if the new size fits better, if it doesn't then move the cursor back to the picker and so on. It's a lot of unnecessary mouse movement. With the Touch Bar, you just leave the cursor where you want it on the image and use the slider on the Touch Bar instead, while you can see the changing brush size live on-screen instead of having to move the cursor back and forth.
Safari. Namely, the visual tab picker and the option to activate PiP even on websites that normally prevent you from doing so (looking at you, Netflix). 'nuff said.
The color picker on the Touch Bar is actually really convenient, I oftentimes prefer it over the on-screen one. I especially like that you can just tap and hold on the button for the color picker and then slide your finger to the desired shortcut-color, which is a few taps/clicks less then first looking for the tiny color rectangle on-screen, clicking it, selecting the desired color there and closing it again.
The video timeline in video apps. I love how the Touch Bar gives you an indication on where in a video you are and how much time is remaining even when the on-screen controls for that are hidden. You know these situations where you're watching a long movie or YouTube video in fullscreen and flick the mouse around just to see how long it's still going? I do that a lot less since the Touch Bar now provides that information. (I only wish that you could turn off how the Touch Bar automatically dims after 60 seconds for these kind of purposes.)
The QuickLook features. I especially like how previewing a long pdf-document will give you miniatures of the pdf pages right on the Touch Bar and I'm genuinely baffled that Apple didn't put the same functionality into Preview. The timelines for movies and waveforms for audio files are pretty useful too.
Another underrated feature: The book timeline in iBooks. Now I'm an avid eBook reader though I read on my iPhone or iPad most of the time, but I can't help but appreciate how simple yet well thought-out the "timeline" in an open eBook is that immediately gives you a clue where in the book you are and even shows the different chapters. Otherwise if you want to check your position an in eBook in iBooks, you have to move your cursor to the bottom area so the scroller becomes visible and then estimate how far through the book that is, which isn't very intuitive or practical. The Touch Bar always shows that information in a subtle yet much more readable way.
The image miniature bar in the Photos App. Another no-brainer: it not only provides you visual clues when in full-screen to the photos before and after the one you're viewing, but using it to scroll through large amounts of photos is actually fairly fast yet extremely precise, it adds a whole new layer to the navigation in the Photos app. I think these sort of timelines and sliders are where the Touch Bar is at its best: not when it's replicating keyboard shortcuts, but when it gives you completely new navigation elements that aren't feasible for on-screen controls and profit from the speed, precision and intuitiveness of a horizontal touch input with your finger.
The new Command + Shift + 5 screenshot/screen recording tools in Mojave. What I like particularly about this is that when recording a video of your screen that way, the Touch Bar will steadily show you the current file size that this recording up to the current point will take. Previously, I'd usually have no idea how long a recording will be until it's actually finished, which can be problematic since the file size can be of crucial importance depending on what you want to do with the file (for example, if you want to upload or share the screen recording with someone, then it usually can't be overly large).
The different formatting tools in apps like Pages, Numbers, Notes, Microsoft Word/Excel etc. Now hear me out, making a text bold for example won't ever be something that I can see myself using the Touch Bar for since the pretty much universal Command + B shortcut is just faster, but what about stuff that you don't know the shortcuts of because you simply don't use them so often? What if you want to format a paragraph of text as a subsection in Word or as a numbered list with Roman numerals with brackets in Pages? These things might have keyboard shortcuts, but are you really going to learn them if you only use them once in a while and if they oftentimes aren't even universal between applications? These are the sort of things where the Touch Bar actions for it come in handy.
Honorable mention: the Emoji picker. Now before you pull out your pitchforks: no, this is not something that absolutely needs the Touch Bar, and I honestly find it a little silly that Apple put so much emphasis on it during the original Touch Bar presentation, but it's just a little nicer and faster to select emojis in this beautiful list with large icons instead of fiddling around with the tiny on-screen emoji picker. I honestly use emojis much more on my MacBook Pro than on my iMac in WhatsApp/iMessage conversations because of the additional convenience.
Also OP I definitely agree with your assessment about the Touch Bar timeline in the Calendar app. I don't use that app very often on my Mac but I think it's another good example of how the Touch Bar is just so suitable for these timeline-ish controls that oftentimes feel misplaced/impractical on-screen.
In all fairness, I don't use each of those features every single day, and the Touch Bar is not an absolute must-have for me – but it's definitely a nice-to-have. There are also many apps where I just don't use it at all because it provides nothing useful, but I think some type of apps just don't have very good functions that can be put on the Touch Bar. I.e. if all the Touch Bar can get in an app is a row of buttons that do things that all have keyboard shortcuts, then it's naturally going to be less useful/interesting there if you already know these shortcuts. But it's these apps that put some new dimensions of interaction or useful visual information onto the Touch Bar where it IMO really shines.
