This has been discussed many times on the forums before. I'm a big fan of Chromebooks, because like the vast majority of computer users, I do almost all of my computer activity in a browser. That includes work (remote access of my hospital's electronic charting system via Citrix), productivity (Google Docs/Sheets), leisure (Google Play Music, Google Play Movies, especially when casting to a Chromecast), and AC forum activity. Although I do have a Windows 10 PC, I do about 98% of computer activity on the Chromebook. Here's a rundown on things I like about it:
1. Fast and lightweight: Recent Chromebooks perform well, because there are no unnecessary Windows processes bogging things down. It literally boots up in 7 seconds, and I'm ready to start working in about 15 seconds. Chromebooks that have the better processors (like Haswell or Broadwell), along with 4 GB of RAM, can function smoothly with many open tabs.
2. Tight integration with Google services: I'm all in with Google, and Chromebooks make it easy to access your Google Drive (as if it were just another hard drive on the system), along with all other Google services.
3. Security: No need for antivirus/security programs, which often bog down Windows PCs. In addition, if I lose my Chromebook, I can rest assured that no one else can access my sensitive data, since it's all in the cloud. All I have to do is change my Google password.
4. Value: You can get an excellent Chromebook brand new for under $300, and refurbished under $200. My 15" full HD Acer Chromebook with 4 GB of RAM and a fast Broadwell processor was just $179. Any comparably priced Windows laptop will lag behind significantly in performance.
5. Battery life: Most Chromebooks will go at least 6-8 hours on a single charge, which is hard to find on a similarly priced Windows laptop.
6. Fast system updates: While a system update is downloading in the background, I only notice the faintest of hiccups. Installation of the update is as simple as rebooting, which again takes 7 seconds. Compare this to Windows PCs, which can take upwards of 30 to 60 minutes to complete multiple updates (longer if you haven't used it in a little while).
Regarding your specific concerns:
1. Chromebooks can in fact do a lot while offline. Documents and photos can be edited, music and movies can be played (if downloaded or cached beforehand). It's true that you can't browse without an internet connection, but that of course applies to PCs as well. These days, most people will use whatever laptop they have where there's a wi-fi connection, and if there isn't, that's what your phone's hotspot is for.
2. There usually is not a need to run a "real" program if the same thing can be achieved on the web. I don't need Word or Libre Office because Google Docs and Sheets do what I need (and I would guess that most people who have Microsoft Office use only about 15% of its features overall anyway). Photoshop is a common criticism, but (a) there are good web-based photo editing sites like Pixlr, (b) Adobe is working on a Photoshop for Chromebooks (
https://edex.adobe.com/projectphotoshopstreaming), and (c) the full Photoshop PC program is so huge and resource-consuming that you'd need a much more expensive high end PC to get any decent use out of it. Running high end games is definitely a weak point of Chromebooks, but then again, you're not going to play high end games on a cheap Windows laptop either.
3. Tablets aren't a good replacement for a Chromebook if you're interested in doing a lot of web browsing, because no matter how powerful the Android tablet is, the browser will always be slower than Chrome on a PC or Chromebook.
That being said, can a Chromebook completely replace a PC? No, which is why I still (reluctantly) have my big clunky Windows PC sitting on my desk. The main time I fire it up these days is to download a podcast on iTunes that I can't find anywhere else (don't get me started on iTunes

). Still, slowly but surely, the things I used to rely on the PC for are being taken care of in the cloud. I uploaded my entire photo library to Google Photos, so I have no real need to store them on the hard drive as well. My entire music library has also been uploaded to Google Play Music.
Are Chromebooks for everyone? No, but I would argue that many many people would find them quite useful. You sound like your mind's already made up, but if you ever get a chance, try spending a few weeks playing around with one---you might end up being pleasantly surprised.