The promise of Agile is that you can release quality code on a regular tempo. The features may not yet be fully polished but you can drive small incremental releases with some set of correct+desired behavior and focus on improvements to critical areas and robustness in longer arcs as long as the core does the thing you really need it to do. Sometimes you have to come up with an equally incremental path towards the Big Refactor you want, setting up dominoes cycle after cycle till you can knock them down at once, but it can and has been done. You still need to prioritize quality and may have to be political about how you do it, and you still need management buy-in because you will not move as fast as a team throwing things against the wall -- but you'll also never actually hit a wall, or if you do it will be more of a speed bump, which is the selling point.
Edit this really has nothing to do with AI. This can be done 100% by hand, 100% by massively parallel agentic swarms, or anywhere in between. It's about process, planning, and the people (yes exclusively people) involved.