But this reminded me of cases where nature rebounded spectacularly beyond all expectation: Chernobyl and Fukushima. So why are they recovering so well, and some other areas not? What's different? Maybe the radiation. Maybe the size. Maybe the the very serious ban on humans, that's a good bet. It would be worth comparing.
Meanwhile, I think the best thing we could do for rewilding is to apply copious amounts of organic matter -- manure, compost, humus, even just tilling under cover crops -- to restore nutrients and build soil before attempting to reintroduce native species. Hell, sow it with alfalfa and let a herd of bison shit on it for a few years. You're not going to hack up old farmland any worse than it already is, and you might manage enough repair to give the restoration a better chance.