[tangent128]

If there's "too much" lag or packet loss, delay-based netcode will also become unplayable; the difference is that rollback has more tools to address bad connections, so that rollback is often not even visible:

- predicting that the buttons held down in frame X will be the buttons held down in frame X+1 is actually a pretty good heuristic

- in fighting games, changing directions and attacking generally have windup animations, so if a correction skips a few of the initial animation frames, it still hasn't diverged the overall game state much

- even in bad connections, you still have control of your character; the game doesn't freeze and take you out of the flow (this can be subjective)

- hybrid approaches are possible, where a small fixed delay is used in addition to rollback; short enough to not be obvious to the player, but long enough to avoid rollback in the cases where delay would be sufficient. (delay-based netcode is not good intercontinentally anyways due to the necessary delay for synchronization becoming obvious input lag)

As for why rollback is rarer, yes, it is more difficult; it usually requires a fully deterministic game engine with the ability to snapshot and restore game state, which can be a very intensive retrofit if you didn't design it in from the start.