> Chess champions before Magnus would’ve had books of strategies to learn from as well, thereby benefiting from the time spent of players long gone.
While agreed on the hyperbole, we're talking about something, in this case learning toward mastery, whose rate of progression is non-linear. There may well be a phase change point(s) where the character of ones ability changes given enough practice or level of knowledge.
Digital technologies augment us mentally and reduce the cost (whether time, effort, or minimum inherent ability) of getting to this "phase change" level. Playing actual games against AI opponents is much more effective as practice than reading strategy books. Being able to tune the AI opponents strategy and practice under realistic conditions against different "styles" of play is something that was much harder to achieve even a few decades ago and would have taken much more time and money.
This also barely scratches the surface of what more specialized software (in this case for competitive chess players, but also in many other areas) can do. A bit of hyperbole warranted here. :-)