I would actually say that playing sub (on live, and likely in mop) properly is complex, and for the reasons you listed. I would call it hard, by the standards of wow rotations.
As much as I dislike the SangV change, I don't think that it is directly comparable. Currently, sub tries very hard to refresh with minimal clipping- you get within a couple seconds of recup going away and sure, fine, refresh it because you get the 32 second one- rupture won't feel like this though. You'll want a five point rupture every time the existing rupture goes away, like RIGHT then. Since HAT is still a thing, this will require proper play to land that rupture. Of course this would also be true of rupture just did enough damage to be worth casting, like they should do instead of tying our hands like this, but the point I'm making is- this mechanic isn't bad like Hunger for Blood was bad. Hunger you could put up at any time, had a long duration, felt like a chore. A bad rogue could just press it whenever nothing else was going on, a good rogue didn't gain much by landing it just at expiry. With a powerful rupture, or with the current design Blizzard has of rupture falling off gimping us, you'll have many opportunities to land that clutch dot correctly.