I agree with you that running an app in the terminal doesn’t always show the dependencies. But, one can find the dependencies in the control file. Or, after installing through synaptic. Btw, please have a look at any app inside /snap folder, see what dependencies are needed. Some snap app developers forget some of these dependencies, so while execution of that snap app, it looks for it, slowing down the start of it.
Anyway, I am for self contained apps/packages, but I think they should be smaller, or just about few kbs/mbs larger than the deb equivalent. I’ve been looking into this area, before snaps came into being. I was expecting an app/package that I can keep in a USB stick, take with me and open in any Linux distro. And, without demanding the other person to install a special app, snapd ubuntu core or else. As, you know there are public computers, where you can use a usb stick and some of them allow an outside application to run from it. The question is about portability, more than anything else.
All right, to check this out in another OS platform, I installed few apps in one Windows 10 laptop, copied the relevant app folders to a usb stick, purged those apps from the 1st laptop and plugged usb stick into another Windows 10 laptop. These apps ran well in the 2nd laptop. Then, plugged the usb stick to the 1st laptop. They ran well in the 1st laptop too. They created their own configs in the both laptops. They are quite large applications; GIMP 2.10.10, LibreOffice 6.3.2, Calibre 3.4.2. and some other apps. It took sometime to reply because of this.
You just can’t do this with snaps on another Linux distro, without a special programs and ubuntu core etc installed in it. You can’t download a snap app, only install it. It goes to root, not to one’s home folder.
Found out quite a few things on this. Enough experimenting on snaps for me.