People assume agile teams skip the planning. In my experience it's the opposite. I plan more as an agile lead than I ever did on a waterfall project. The difference is when.
I've seen teams that do all their planning in a single quarterly session. Detailed roadmaps, ticket-level breakdowns, the lot. Then those tickets flow straight into sprints with little or no further thought. By the time the work reaches a developer, the plan is months old and based on what was true at the start of the quarter, not what is true now.
The cracks tend to show up in review. Issues that should have been spotted before a single line of code was written instead surface after the work is built. That's one of the most expensive places to catch a problem. The cheapest place is in a planning conversation, when nothing has been committed yet and a five-minute chat can change the entire approach.
People look at a sprint planning session and assume that's all the thinking that happens. They miss that there are at least three planning passes before code is written. Roadmap, shaping, refinement. Each one with better information than the last.
Waterfall does the most planning at the exact moment it has the least information to plan with. That's the bit that catches people off guard when I lay it out.
I plan more in agile, not less. I just don't pretend I knew everything in January about what would matter in April.