"We're a TV station, not a data analysis service - it's not our problem if that DVD with a commercial you sent in was broken in half; we'll just emit 10 seconds of white noise and charge you the normal screen time rate, even though we could have you provide another media." It's the approach you're presenting. Sure, a sync program is a sync program, but it's not uncommon at all for programs to interface with each other for a combined purpose.
1. It's not at all likely the remote location has ransomware too if it's on a different platform or hosting service altogether.
2. Is it practical to have my ENTIRE file collection in the archive folder? I have yet to use Resilio, so you'll have to judge for me.
3. Don't like a feature? Turn it off. Don't like confirmation messages popping up? Turn them off. "Thanks for asking, but I am, in fact, updating large numbers of files right now. Stop asking for, say, a day."
Nothing's wrong with using an AV scanner, that's a ridiculous question. Not all viruses and ransomware get detected quickly enough for everyone to get their AV databases updated. Pretty much everyone's running Windows Defender now, and look, ransomware attacks spread like wildfire anyway. So apparently not all AV packages are equal.
Then there's the accidental deletion, of course, with no malware involved. Oops, I pressed the wrong button, and the program I was using adopted the approach you outlined yourself: it wasn't built to prevent the user doing damage to their files, so they didn't build any "are you sure?" messages in. Now my files are gone... ah, but they're on my mobile. DOH! Not anymore! STOP! ABORT! Too late.
So tell me, is it really that absurd to propose some sort of plugin solution (no feature creep) that could prevent or otherwise influence syncing in specific cases?