Battery do degrade over time, but the phone speed nerf was spread to many phones were battery degradation was far too little to cause the kind of disruption you're talking about. A theoretical concern that was marginal at best in the actual fleet of phone was used as an excuse for shady behavior (And that shady behavior got them a fine in France before they reverted the patch here).

Also, I don't understand why you're linking to an article that contradicts you. It reminded me something I had forgotten though: that eventually Apple (partially). caved and made this behavior opt-out for everyone.