Software does require on-going effort to remain in the market, even if no new features are added: security vulnerabilities come to light; bugs are fixed; support for new or updated operating systems and other software and hardware is added; etc. In fact I'd prefer that developers spent more time fixing existing issues rather than adding new features because, inevitably, adding new features adds new bugs, often faster than they can fix the old ones. It sounds great to say software shouldn't have any vulternabilities or bugs, so the vendors should fix these for free, but let's be realisitic.
So I don't see software subscriptions models as being inherently bad. The problem with Adobe is that the price is so extremely high. It seems like they're trading on their dominant market position to extract all they can from their customers, rather than charging what it costs to maintain their products plus a fair margin. They're breeding competitors and eventually it will bite them.