However, I agree with you a billion percent between apps. I'm sure I've copied text from a webpage into a document 10,000 times, and not a single time have I ever wanted the font or size or color preserved.
Just think it's an important distinction to preserve.
I will say, sometimes I do find myself wondering whether something was copied as plain text or as formatted text, or whether I pasted the previous thing before going to copy another.
I really like what Apple has done with screenshots — a thumbnail hovers in a pop-up window in the corner of the screen for a bit. Doing something similar with the clipboard might not be the worst idea — after cut/copy, a thumbnail hovers in the corner until you paste, or until 15s have passed.
The fact that "copy" results in zero visual confirmation whatsoever does seem to be a bit of a violation of standard UX guidelines. Heck, even a visual effect like a flash and quick zoom-fade-out of the copied content feels like it would be helpful.
I do think in the early days (for me, this is the 90s) I had failures that weren't fat-fingering, the keypress just not registering. Maybe the wrong window has had focus once or twice too in some weird scenarios.
That your keypress registered. You held down the modifier and you think you hit "C", but did you actually? For unfathomable reasons, when you copy text, there's no visual or other confirmation that anything has happened.
If it takes you a long time to navigate to where you want to paste (scroll a lot in an editor, juggle windows, etc.), it's a bummer to get there and learn that your clipboard doesn't have the text on. You have to make another round trip.
While I don’t paste in place of my copy, I do use Cmd+Ctrl+V to paste in Terminal (which escapes all “special” characters with a backslash) to avoid trouble.
To counter your first use case, if I'm copy-pasting the second word (say it's a complicated name) of a heading to reuse in a paragraph, I don't want that paragraph to be another heading. In another universe, the geniuses who coded the editor realized that "no one will ever want a word in the middle of the paragraph to be in a different font, in a different color and with a different background color because they copied it like that from a website with that formatting".
However, I would appreciate a setting that would let me arbitrarily switch between dragging vs reselecting already selected text.
Sometimes because I want to keep what’s in my clipboard already; other times because it’s sensitive enough data that I don’t necessarily trust all running applications with (the threat primarily being an application incidentally logging/persisting it as part of some “helpful” feature, not outright malware).