You can test a lot longer than a few weeks with replay if you have the right data. And the data format is pretty obvious, so pretty much any data can be made into the right data with a little effort.
No test environment does long tick-driven tests with variable parameters etc - it would take years.
I know it can test longer then a few weeks, took me about 6 hours to do market replay for just 3 months( have to change contracts, cant skip weekends, and only runs at 500x speed).
