Sure but most people say that you have a better chance at recovering the earlier on in your illness.
I'm not sure whether that's actually valid. Some people might have ME that goes away early, regardless of whatever treatments or lifestyles are tried. Others might have ME that responds better to treatment, and they manage to find that treatment early rather than late. Other people have ME that sinks its nasty claws in and refuses to let go. I'm unaware of any properly-done study that shows that early treatments, whether aggressive resting or whatever else, is effective at reducing long-term ME severity. Given the lack of a marker and effective measurements of symptoms, I don't see how anyone could provide reliable statistical evidence.
Does ME 'dig its nasty claws in deeper' the longer the victim goes without practicing pacing, aggressive resting, avoidance of factors, etc? I don't know, and I doubt that anyone else does either, since we don't know the mechanisms involved.
I still think the question about whether aggressive resting will be better than not practicing aggressive resting is just a coin flip: 50/50. Aggressive physical exertion is more likely to cause harm, but isn't guaranteed to be not effective as a treatment. No guarantees anywhere.
FWIW, on my morning walk AI was thinking about this thread and I couldn't remember any of my experiments with avoiding factors for a long period that had a long-term beneficial result. I avoided some foods for a couple of years, and was able to consume them safely again, but was that because I avoided them or just a change that would have happened even without avoidance? I'm back to intolerance of some of those foods again, so I think it's just how ME changes over time. ME is a disease that you can't make long-term projections about.