Chainsuck on a relatively little used bike?

My fatbike doesn't get used enough and is tempting me to part with it for some other toy. The trouble is the gears just aren't quite right.

Before I started tinkering, the gears on the back tended to ghost shift briefly under load.

I started looking at it and firstly noticed the chain was very dry so thoroughly lubed it, but it still skipped even in the stand. I noticed the front mech wasn't very well set up, rubbing against the chain when it shouldn't. Didn't think that would be it but decided to fix it anyway, that's now set up properly but the back end still misbehaved.

Checked the gear cable was running freely and not dragging.

Checked the hanger alignment (via a length of wood and a spirit level, no professional tool) and it seemed slightly off so whipped that off and straightened it up. Reassembled and it's stopped skipping, but the derailleur cage is getting pulled forward very slightly by chain suck and then releasing.

On the road / trail it's not noticeable but in the stand it's very obvious and I'd like to sort it before sale, but not sure what to go for next. Front chainrings don't look too bad but would seem to be the next port of call? cassette looks unworn.

Really the perplexing thing for me is that this bike probably hasn't done more than 1000 or so miles, mostly on road or dry trails and I don't get how the chainrings can be shot whilst the cassette is perfect. I changed the drivetrain less than chainrings shortly after I bought it, upgrading it to 9 speed. I'm left wondering if the original chainrings are so cheap that they are shot when the rest of the drivetrain is barely run in.. they look a bit worn but not desperately. Equipment level is basic (Voodoo Wazoo - alivio rear mech is about the only named item on it except for upgrades).