They absolutely plan where they want to be in 3-6 months -- they're generally quarterly OKR's -- but the only way they consistently achieve their targets is with weekly or biweekly readjustments.
They do, and if you need to adjust a project you don't need 10 hours of weekly planning meetings (the Linux kernel developers don't need it, so your CRUD app developers don't either).
The higher you go, the less agile it gets, because that's a horrible way to develop software, or any high-skill professional service or product.
